Bayern centre-backs doubtful for Lyon clash
The pair suffered calf injuries in Bayern's 1-1 draw at Borussia Moenchengladbach - Argentina defender Demichelis limping off just after half-time, while Belgium's Van Buyten went off after 64 minutes.
"I took a knock on the calf," revealed Van Buyten shortly after the final whistle. "Now it is worse than when I came off."
Both players are now facing a race against time to be fit for the match in Lyon with Bayern boss Louis van Gaal keeping his fingers crossed.
"I hope that at least one of the pair is fit for Tuesday," said van Gaal.
Youngster Holger Badstuber, who has been outstanding in his first season in the first team and has played his way to the verge of the Germany squad, could be moved from the left side to the centre of defence as cover.
Bayern hold a 1-0 lead from Wednesday's first leg after Dutch winger Arjen Robben scored a second-half winner.