The Tottenham forward's recovery from a serious cartilage injury became so difficult that he spent the summer consulting other specialists about an operation that could have kept him out for another 18 months.
The 26-year-old ultimately rejected the procedure and has now returned to action for Tottenham and Sweden after almost two years away from international football.
Speaking to Swedish newspaper Fotbollskanalen, Kulusevski explained that his initial treatment failed, while a subsequent operation also failed to resolve the problem.
"I spent the whole summer talking to other doctors about having another operation. It would have been a knee transplant. I would have exchanged my knee for someone else's."
The prospect was frightening, with doctors telling him that nobody had previously returned from the procedure and putting his chances of success at 50-50.
"I said no. If I'm in pain when I play, then I'll have to play with pain."
Kulusevski said the proposed transplant would have meant another year and a half away from football. He was determined to find another solution, despite the uncertainty surrounding his recovery.
The injury affected even ordinary daily activities. Despite spending up to 10 hours a day training, he struggled to make progress and began to question whether his career was over.
"I was training ten hours a day, but it wasn't working. It didn't matter what I did. That's when I started thinking: 'If it's over, it's over.'"
Eventually, he felt he had to prepare his family for the possibility that he would not return.
"I had to tell my mum: 'I don't think it's going to work.'"
His mother reassured him that the family's love would not depend on his football career. Kulusevski also considered what life might look like without the game, imagining moving to an island and spending time with his family. He said having his daughter helped him through the most difficult period.
Support from Zlatan Ibrahimovic and former Tottenham team-mate Ivan Perisic also proved important. Both encouraged him to seek help from a specialist in Serbia.
"Zlatan and Perisic wanted me to go there. I went, and the Serbian doctor was important for me."
"He said: 'Don't think about other operations, this is what we're going to do.'"
Kulusevski believes the eventual breakthrough came through specialist work involving his nervous system, rather than another operation. He continues to work with a group of experts, and acknowledges that his knee can still feel different on certain days.
The forward has also spoken about disappointment with some of the people around him during the rehabilitation process, including at Tottenham.
"There were many who didn't believe it, many were sceptical. Even at the club."
"I've been disappointed in people during this period, but at the same time I have to forgive everything."
"Sometimes you wish you'd received more help and so on. But at the same time, I understand we're all part of a business."
Despite those frustrations, he insists he has moved on and remains happy at Tottenham.
"I've moved on and I love being at the club. I received a really good welcome when I came back."
His return has also brought him back into the Sweden squad for the first time since November 2024. He expects to be given around 30 minutes in each of the upcoming Nations League matches against Bosnia and Herzegovina and Poland.
"I'll get to play some minutes in both games. Around 30 minutes in each. That's what’s been said. It's better than zero, so I'm happy."
Kulusevski joked that he felt capable of playing the full 90 minutes in both fixtures, but accepted that the decision rests with head coach Graham Potter and the medical staff.
"It's a dream. It's what I've worked hard for. I'm just happy, and I'm a competitive person. I want to get out there, compete and show who I am."
He also identified the number 10 role as his preferred position, although he is prepared to adapt if asked to play on the wing.
After everything he has endured, Kulusevski is trying to rediscover the uncomplicated enjoyment he had as a child.
"I'm trying to get rid of everything and become that little boy again. Little Dejan, who was eight years old and knew nothing, but knew how to play football."
For Tottenham, his return is hugely encouraging, but the severity of the injury and the length of his rehabilitation mean his workload will need careful management. The immediate priority is to build his fitness gradually after a recovery that, at one stage, left him fearing his career was over.