Bayern Munich have announced that midfielder Luiz Gustavo has undergone successful surgery on his groin.
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Gustavo, 25, has been sidelined since sustaining the problem in Bayern's 3-0 win over Hamburg, and it is unclear how long he will be sidelined for - although it is anticipated he will be absent for the clash against rivals Borussia Dortmund on December 1.
"I can't predict how long he will be out," Bayern boss Jupp Heynckes said. "It is a severe blow for us. He has played a very good season so far and is an important player in our system. I hope he gets well soon and returns to the squad as soon as possible."
Gustavo has so far enjoyed an impressive campaign for Bayern, scoring three goals in nine Bundesliga appearances and featuring in every Champions League match until his injury ahead of the recent Lille game.
Bayern will also be without Arjen Robben for Tuesday's meeting with Valencia. The Netherlands international tore a muscle in his country's friendly against Germany last week and will be sidelined for another two weeks, according to kicker.
France international Franck Ribery could return against Valencia, despite his bruised ribs. "It is not an easy injury," said Ribery. "But I have to play. It is a very important game for us. A win would be fantastic for us."
Bayern currently are on top of their Champions League group F, but last season's finalists only have a three-point advantage on BATE, who are currently ranked third and face Lille in the group's other match.