Bayern Munich midfielder Thiago may not play again this year after suffering what head coach Jupp Heynckes described as "a heavy thigh strain" in the 2-1 win away to Anderlecht in the UEFA Champions League on Wednesday.
The Spain international was helped from the field of play at the Constant Vanden Stock Stadium by the Bayern medical staff, before being replaced by Real Madrid loanee James Rodriguez late in the first half.
Dutch winger Arjen Robben also picked up a knock in the Belgian capital, although Heynckes did not appear overly concerned. "I don't think it's that bad; just a minor muscular problem."
Bayern, who have won their last eight matches in all competitions, next travel to Borussia Mönchengladbach on Saturday evening (kick-off 18:30CET/ 17:30GMT).