Bolton keeper Jussi Jaaskelainen will miss the rest of the season because of a back problem picked up in the warm-up against Sporting Lisbon on 6 March.
It means the Finn, 32, may have played his last game for Bolton as he is out of contract at the end of the season.
Trotters boss Gary Megson, who is using Ali Al Habsi as cover in goal, told the club website: "Jussi needs six weeks of rest to try to resolve this problem.
"He needs some form of surgery. Either way, his season is over."
Bolton are currently third from bottom in the Premier League and face a visit to leaders Manchester United on Wednesday.
Since Jaaskelainen suffered the injury before the Uefa Cup tie, Al Habsi has taken over from the Finland international in goal, while the experienced Ian Walker is also available.
Jaaskelainen joined Bolton in a £100,000 deal from VPS Vaasa in 1997 but turned down a new contract with the club last summer.
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