However, his body rejected the organ and he subsequently received a second kidney from his father.
Klasnic’s second operation was a success, and he soon returned to football, becoming the first player ever to compete at a major international tournament after such a medical procedure when he was picked to represent Croatia at Euro 2008.
However, in September of 2016, Klasnic was deemed critically ill after his kidney failed, and he now spends three days a week on dialysis in hospital.
"I thought I'd have a shorter life or something,” he said during a documentary aired by NDR, a German television station. “I have to accept the fate of it is, go on dialysis, but maybe it’ll come and there’ll be a happy ending.
“And that would be that successful third transplantation and me no longer having to go on dialysis.
"The hardest part is that my mother lost a kidney, and I am grateful to my parents a lot."
Klasnic helped Bremen win both the Bundesliga and the DFB-Pokal in the 2003-04 season, scoring 13 goals despite his illness.
Following the first failed transplant, Klasnic took legal action against his doctors, explaining: "I'm no expert, or doctor, but I could see that something was wrong [with their therapy]. They have to see too.
"My mother's kidney was installed, but something was wrong.”
A second transplant followed, this time from his father, but Klasnic insisted on moving hospitals - and even gave a false name, Uwe Seeler, upon arrival.
He added: "I'm a football player, and football players are superstitious. So I did not want a new operation carried out in Bremen, even on the same day. We did it on Friday in Hanover instead."
He returned to the field just six months later, but he is now again waiting for another donor. His brother, Joseph, does not qualify.
Despite his condition, Klasnic continues to play football once a week, and hopes to return to normal soon. He adds: "I wish for the new kidney and life without difficulty."