MUNICH, Germany (Reuters) -- Bayern Munich central defender Holger Badstuber is doubtful for the Champions League Group A match against Manchester City on Tuesday, coach Jupp Heynckes said.

Badstuber, who has been instrumental in Bayern's run of nine straight games in all competitions without conceding a goal, is suffering with flu, Heynckes told reporters on Monday.

"A decision (on whether he will play) will be taken shortly before the game," said the coach, adding Daniel van Buyten could replace him.

Centre back Jerome Boateng, who was rested in Bayern's 3-0 win over Bayer Leverkusen on Saturday, would "naturally" start, Heynckes said.

Heynckes said he expected a much tougher game than what Bayern had encountered until now this season with the two teams "testing their strengths."

"But we also have several players on the pitch who command respect," he said.

Bayern beat Villarreal 2-0 in Spain in their group opener while competition debutants City drew 1-1 at home against Napoli.

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