Bayern Munich and Schalke 04 great Olaf Thon believes that Louis van Gaal's side need to strengthen the squad, with players such as Breno and Danijel Pranjic not good enough for the champions.
"Maybe Bayern need to strengthen their squad as early as January - especially in the defence. For example, I don't believe that Breno or Danijel Pranjic are good enough for Bayern - especially Breno," he wrote in his column in tz.
"He is immobile and clumsy, like a foreign body. I hope that Bayern get a grip on their defence in the winter."
Thon also refused to rule out the prospect of Bayern retaining their title, despite the sizeable lead amassed by Borussia Dortmund.
"Mainz do not look as strong as a few weeks ago and I am sure that Dortmund will drop points throughout the season. Bayern will still have a say in the destination of the title."
Brazilian centre-back Breno recently returned from a cruciate ligament injury against his former club Nuernberg and he could force Daniel van Buyten's departure from the Allianz Arena.