Thomas Muller has put Manchester United on red alert by admitting he is not happy at Bayern Munich.

Muller was an unused substitute as Bayern Munich beat RB Leipzig 3-0 last month in their last game before their winter break. The Germany international has made 22 appearances for Bayern this season but does not appear to fit into new boss Carlo Ancelotti’s side.

And Muller could not hide his frustration when asked about his situation at the Allianz Arena.

“The last game against Leipzig was not optimal for me personally, since I did not play,” Muller told German newspaper Bild.

“There was more space than in the games before. It was a game I could have enjoyed.

“Of course, I’m not sitting there with a grin on the bench.”

Manchester United are long-term admirers of Muller, who has won every honour available to him at club and country. Former United boss Louis van Gaal tried to sign Muller during his tenure at Old Trafford but had to settle for his former Bayern team-mate Bastian Schweinsteiger instead.

Red Devils manager Jose Mourinho may also be interested in the 27-year-old were he to become available for transfer.

Bayern Munich legend Lothar Matthaus recently cast doubt over Muller’s future by admitting he doesn’t really fit in under Ancelotti. “There is not really a position in Ancelotti’s formation that suits him,” Matthaus told Bild.

Muller, 28, has only scored a single Bundesliga goal this season, ending his scoring drought in the league after 999 minutes with a strike in Bayern’s 5-0 win against Wolfsburg last month. He also failed to score for Germany at Euro 2016.

Despite ending his goal drought against Wolfsburg last month, the Germany international was dropped to the bench for Bayern’s next home game – a 3-0 win over title challengers RB Leipzig.

Muller has been in and out of the team during the first half of the campaign and has often been substituted before the 70-minute mark when he has started games.

As such, the 27-year-old’s goal tally is way down. He enjoyed the most prolific season of his career in 2015/16 with 32 goals in all competitions, but has just four to show for the first half of 2016/17. Only one has come in the Bundesliga, while another was in the Super Cup.

So far this season, Muller has been used wide on the right, both in a midfield and forward role, as well as high on the left, as a ‘number 10’ and through the middle as a central striker.