Hummels and Lewandowski in training bust-up over tying shoelaces

Bayern are 19 points clear in the Bundesliga table, but tensions often run high in the star-studded squad for starting places.

Temperatures in Munich were well below freezing at Bayern's Saebener Strasse training ground during the angry exchange.

According to German daily Bild, who have a reporter at Bayern training sessions, 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, a team-mate in the exercise, sparking a war of words.

"Lewy, are you serious? You're seriously tying your shoes? Holy shit!," yelled Hummels, a 2014 World Cup winner with Germany.

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 Lewandowski retorting "you constantly lose the ball, you're just talk" and Hummels snapped back "Oh shut up, get lost".

Neither offered to apologise and when the practise game ended, the pair ignored each other.

Bayern have a tricky away league game on Sunday at Freiburg, who are unbeaten in their last six matches at the Schwarzwald Stadion.

Freiburg's ex-Bayern striker Nils Petersen has 12 goals this season, second only to Lewandowski, who has 20 in the Bundesliga, in the league's current top scorers.