Mats Hummels accused Bayern Munich teammate Robert Lewandowski of an 'attitude' problem in a training ground bust-up on Wednesday, reports say.
According to German daily Bild, Hummels and Lewandowski traded insults in a practise game.
When Lewandowski briefly paused to tie his laces, allowing the opposing team to score, Hummels ripped into the Poland star, sparking a war of words.
"Lewy, are you serious? You're seriously tying your shoes?," yelled Hummels.
Lewandowski fired back, "you just lost the ball," to which Hummels replied: "that was a mistake, but with you it's an attitude."
The pair squared off with neither offering to apologise and when the game ended, the pair ignored each other.