Robert Lewandowski and Mats Hummels argued at training on Wednesday, with Hummels accusing his teammate of being sluggish and telling him to "shut up."

Lewandowski decided to tie his shoelaces rather than defend during a training match.

"Lewy, are you serious? You are doing shoelaces? Holy s---," Hummels reportedly said, before Lewandowski replied: "And you've lost the ball."

Hummels later questioned the striker's attitude and Lewandowski responded by questioning Hummels' ability before the defender said: "Shut up. Get lost!"

Hummels and Lewandowski were also teammates previously with Borussia Dortmund.

Hummels played down the incident, saying it was a routine disagreement.

"It's nothing big," he told Bild. "It happens all the time."