Jupp Heynckes says Thiago Alcantara suffered a serious muscular injury during Bayern Munich's 2-1 win over Anderlecht in the Champions League on Wednesday, but Arjen Robben may have escaped more lightly.
Thiago was replaced just before half-time, with Javi Martinez coming on for the midfielder as Bayern shrugged off a slow start to pick up all three points.
Robben, meanwhile, was withdrawn three minutes into the second half.
Speaking after the match, Heynckes revealed the club faced an anxious wait to discover the severity of the Spain star's problem.
"Thiago suffered a serious muscular injury," he told Sky.
Of the veteran Dutchman, Heynckes added: "Robben said he thinks it's not too bad. We have to wait for the diagnosis."
Bayern sporting director Hasan Salihamidzic confirmed the injuries as well, saying that Spaniard could miss a "several months" with his injury.
"There is not a good mood as Thiago is injured and we don't know about Arjen Robben," he said to Sport1.
"Thiago suffered a grave muscular injury. He'll be out for sure longer-term, likely several months."
Heynckes was not completely satisfied with his side despite the victory, a result that keeps them second in Group B, three points behind Paris Saint-Germain, ahead of a clash with Unai Emery's side at the Allianz Arena next month.
Anderlecht had the better of the chances in the first half but the visitors won it after the break thanks to goals from Robert Lewandowski and Corentin Tolisso.
However, Heynckes felt Bayern were complacent against an Anderlecht side yet to pick up a point in the group stages.
"We played very badly in the first half and gave away two or three big chances," he added.
"Of course you need to be direct about that with the team. We went into the game thinking it would be an easy game because our opponents didn't have a point in the group. We gave the ball away far too often and they had too much space."
Defender Jerome Boateng was also displeased with the side's showing in the first 45.
"It was the worst game since a long time," he told reporters. "We slept the whole first half. Anderlecht was more aggressive, quicker.
"We can't be satisfied, that's not the way we want to play. Every single player was bad today. Everybody has to look critically to himself.
"The coach warned us before, but we have not been focused nor aggressive. After today we have to start at the beginning."