Bayern Munich chairman Karl-Heinz Rummenigge questioned the form of Jerome Boateng following the 3-2 Champions League defeat to Rostov.
Boateng produced a poor display in the Bundesliga champions' shock loss in Russia, with forward Sardar Azmoun leaving the centre-back sprawled on the turf as he danced his way through Bayern's defence to score the home side's first goal.
The 28-year-old was forced off with a thigh injury in the second half and is set for further tests on the problem once the team arrive back in Munich on Thursday.
Rummenigge, however, was far from impressed with his performance despite his apparent muscle problem.
"It stands out a little bit," he told Sky. "Jerome needs to find a bit more calm again.
"I think it is too much for him since the summer. It would be for the benefit of him and the benefit of the club if he could come 'back to earth' a little bit."
Bayern's defeat, coupled with Atletico Madrid's 2-0 win over PSV, means Carlo Ancelotti's side will progress to the last 16 as runners-up in Group D.