Bayern Munich has confirmed Medhi Benatia faces a spell out of action after suffering a thigh injury.
The Moroccan center back limped off 36 minutes into the first half of Saturday's 2-1 win over Hoffenheim and was promptly replaced by Rafinha.
Bayern has since confirmed that Benatia has damaged a hamstring muscle but would not speculate on how long he will be out of action.
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Sporting director Matthias Sammer admitted on Saturday that the injury did not look good.
"We think it's a muscular problem and I don't think it's just a minor injury," the former Germany international is quoted as saying by Abendzeitung Munchen.
Benatia is now expected to miss next Saturday's visit of Bayer Leverkusen, which finished third in last season's Bundesliga.
The unavailability of the former Roma man represents a major defensive headache for coach Pep Guardiola, as the 28-year-old's fellow center half Jerome Boateng was sent off in the 2-1 win at Hoffenheim.
Bayern had found itself a goal down after just nine seconds of play in the team's second Bundesliga outing of the new season, with Kevin Volland opening the scoring for the home side.
However, the German champion deservedly leveled through Thomas Muller just before the break and then maintained its 100 percent record thanks to Robert Lewandowski's last-minute goal.
Sammer admitted afterwards that Bayern is currently struggling to reproduce its very best form, but suggested no new players will be signed before the close of the transfer window.
"The team has seen today how hard it is going to be in the Bundesliga this season," Sammer added. "We still need to find our rhythm with each other. We're still lacking in some areas but the mentality is right. We need to show more cohesion.
"In the transfer window, everything is always possible because it is by nature so irrational. But we are not anxious to change anything too much as our squad is still great."
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