Bayern Munich defender Holger Badstuber faces the prospect of another full year on the sidelines after learning he will need a fourth operation on his injured right knee.
Badstuber tore his cruciate ligaments last December in Bayern's 1-1 draw with Dortmund.
After a first operation, complications necessitated surgery for the second time before a third surgery after he suffered a relapse on his road to recovery.
Now, he has been told that a further operation will be required once his wounds are healed again.
"Until that happens, it could be between three or six months," the 24-year-old, who risks not only missing the entire 2013/14 season, but also next summer's World Cup, told Sport Bild magazine.
"I just hope it is closer to three or four months since I used some of my own cartilage in the operation."
Tissue from Badstuber's left knee will be inserted in his right knee in the operation which will be carried out in the United States as soon as the structure of his operated knee is strong enough for further surgery.
The earliest date for that is October, and with a six-month recovery period to follow, he is almost certain to be out of action for the entire season, if not longer.
The striker, who scored 16 goals last season including a double against Bradford in the play-off semi-finals, has been offered a new contract but has yet to sign.
Rowett is keen to get the matter resolved so that he can look at replacing the 28-year-old should he opt to leave the Pirelli Stadium.
"We made Calvin an offer, which probably wasn't what he was looking for after feeling he had a good season - which he did," Rowett told the club's official website.
"But there is always restraints on what we can offer people and Calvin is one of the top earners.
"He's gone away and had a chat with one or two clubs who are interested in him but he's going to be sought after - he's a very good striker who is 6ft 4ins tall and in our division there aren't many of those about.
"I've had a good chat with him and told him I really want to keep him and that I'll do everything I can to keep him but ultimately it's going to be his decision.
"He either chooses the love and affection we have for him or he carries on looking.
"We really need an answer from Calvin this week so that we don't miss out on other targets should he choose not to re-sign."
