Manchester United are on 'red alert' after Thomas Muller declared he could leave Bayern Munich, reports have claimed.

The German, who is out of contract at the end of the season, rang alarm bells this week when he stated he was not 'fixed' to Bayern, despite spending his entire career at the club.

"I'm not fixed to this club. I have a special relationship, I love Bayern before I started playing for them, he told The Times.

"But when there is a situation where you have to decide maybe to play for a different club, it would be no shame and no problem at all.

"Maybe like with Thiago (Alcantara at Liverpool )."

According to the Daily Star, these comments have reportedly caught the eye of United, who attempted to sign Muller in 2014 when Louis van Gaal was in charge.

The Red Devils are on the hunt for a striker this summer, with Edinson Cavani likely leaving Old Trafford.

Signing Muller, who operates as a wide midfielder, would allow Ole Gunnar Solskjaer to put his faith in Mason Greenwood as his new number nine.