Oliver Glasner puffs his cheeks and starts the search for the right words to explain his emotions as he prepares to return to Crystal Palace for the first time since leaving. There is the small matter of heading back on Sunday with Nottingham Forest to Selhurst Park, where bitterness runs deep over the club seizing Palace’s place in the Europa League last season. Forest’s owner, Evangelos Marinakis, is suing Palace for defamation relating to a banner unfurled by their supporters and the rivalry heightened when Glasner joined Forest in the summer, 40 days after winning the Conference League with Palace.

“I know I will be, but I don’t want to be in the middle of all the comments and the stories about this game,” he says in the boardroom at Forest’s training base. By which point Glasner, a charismatic and intelligent individual who studied for an economics degree while a player in Austria, has turned to Faust, by the German writer Johann Wolfgang von Goethe, to explain how he feels about facing his previous club. “Two hearts are beating in my chest,” he says, tapping his torso, alluding to a line in the classic play. “Here is a little bit similar, because we had a little bit more than two great years [at Palace].”

Glasner led the Eagles to their first major trophies, backing up an FA Cup win at Wembley last year by clinching the Conference League in Leipzig in May, the competition to which Palace were demoted after Forest complained to Uefa about a breach of its multi-club ownership rules. Palace also won the Community Shield for the first time under Glasner. It is owing to that unprecedented success that the Palace chair, Steve Parish, has said he would be mortified if Glasner receives anything but a hero’s welcome.

Glasner hopes the Palace supporters recall fond memories. “They should look back at the emotions they had when they attended the final at Wembley, when they attended the final in Leipzig, when they watched the Community Shield; how much joy they had, how much they enjoyed being a Crystal Palace fan,” he says, keen to stress the timeline of events that led to him joining Forest. “It was not a decision against Crystal Palace, because I decided last October, one year ago, not to sign a new contract. It was then, in the summer, a decision for Nottingham Forest, due to different reasons. Sometimes unexpected things happen in life … there was no plan for me to be Forest manager.”

Glasner, who remains in touch with Parish and has visited him in London, will not apologise for being outspoken. He refers to the February episode when he told Palace supporters to “stay humble” after some had chanted for him to be sacked while on a run of one win in 15 matches, during which they were knocked out of the FA Cup by the part-timers Macclesfield.

“I will never say what everybody wants to hear, I will say it if I think it’s right. And then I have to accept the booing, I have to accept that not everybody is aligned with what I’m doing in my life. I’m now 52, I don’t need to ask everyone if it’s fine what I’m doing … as long as it’s aligned with the law.”

Supremely comfortable in his own skin, Glasner is on good form across more than an hour of conversation, whether discussing working with Marinakis, experimenting with a four-man defence in last weekend’s friendly win over Swansea, or providing the lowdown on some hotly contested recovery sessions: an in-house padel tournament. Nikola Milenkovic and Nicolás Domínguez were champions, beating Glasner and his assistant, Michael Angerschmid, in the final. “I was disappointed that I lost,” Glasner says, smiling. “But Milenkovic and especially Domínguez, an Argentinian, were too good.”

The international break offered Forest breathing space after a disappointing start, time to evaluate. A week on from victory at Aston Villa, Forest crashed to defeat at home to a previously pointless Coventry.

“It’s always in these situations [that] the season is decided,” Glasner says. “In these situations, after losing against Coventry, it’s important how you react. Not on the pitch, but how you react in the club, in the team, all together. Do you stay together? Do you blame each other? Do you look for: ‘Well, it’s [because of] you, it’s [because of] you. It’s always the other ones, it’s never me.’ Then, things don’t change.”

Forest fans can take heart from the fact Glasner also made a slow start to life at Palace, winning none of his opening eight league games. At Eintracht Frankfurt, he won none of his first eight matches but finished the season by hoisting the Europa League trophy in Seville. When Glasner met Marinakis in Athens, discussing the job over a seafood platter in Vouliagmeni, on the outskirts of the city, he advised the Greek owner that there was no quick fix for a team that cycled through four managers and finished 16th last season. “I said: ‘If you expect everything to work within one month, I’m the wrong one, take another one.’ I see things going in the right direction. I feel the messages we are delivering to the players, the things we are demanding are getting more and more natural.”

Three months in, it is still easy to wonder how Glasner ended up here. Externally, joining Forest on a three-year contract was viewed as a surprise, if not a sideways move. He glances at a glossy image on a wall of the City Ground and talks about a similar-sized picture he has in his home office, of him on the balcony of the Frankfurt Römer town hall, 50,000 fans celebrating behind him. “I get goosebumps,” he says. “When I’m considering a club, it’s not just about winning the Premier League. For me, it’s: what is the potential? Is there a real chance to do better with the team? And, at the end, is there potential where I can help to get all this potential to the surface and do better? Is it possible together – because I can’t do anything alone – with the players, with the staff and with the ownership that we can write a chapter that stays in the history books of the club?”

Glasner was on holiday in the serene Austrian lakes with his wife, Bettina, the sun beating down on the water, when the interest from Forest ramped up. “She said: ‘Why are you always looking at your phone?’ [I said:] ‘I’m going to Athens tomorrow.’ She said: ‘Are you crazy? We are here on vacation.’ There were many, many different options in the summer. The one I thought I would do is staying at home, which is why my family was not really pleased with my early decision to leave again … but in that moment when I looked in detail, into the [Forest] squad, and [gathered] my thoughts, I started to get butterflies.”

His enthusiasm for the job is discernible in his voice. Last week, he welcomed grassroots coaches and schoolchildren to training, taking part in a Q&A and putting on a 45-minute session for the kids. “The biggest difference compared to London is that everybody seems to know me,” Glasner says. “Whereas in London you can be quite anonymous; I always took the tube and then maybe there were two or three [supporters who recognised me], and maybe I’d do 10 selfies. But here everybody recognises me and they want to have a few photos.” On Sunday afternoon at Selhurst Park, it is fair to say that there will also be no such invisibility cloak.