Manchester United is on alert after reports from Germany that Borussia Dortmund defender Mats Hummels will be handing his transfer request at the end of the season. Hummels has struggled under his new manager Thomas Tuchel and Bild reported via The Independent that the player is not happy in Dortmund anymore.

The German international and his new boss reportedly had a falling out that is causing his current form to decline. According to Squawka, Hummels has made more defensive errors leading to a goal with three than any other Bundesliga player this campaign.

The Independent noted United's boss Louis Van Gaal is a fan of the 26-year-old defender and has been linked with the Red Devils in the past few years. Hummels admitted this past offseason that it was an honor to be linked with a club like Manchester United.

"When the big clubs like Manchester United come for you, it's a big honour and a good thing. But I decided to stay this year," Hummels said via The Star. He has a contract with The Black and Yellows until 2017.

Bleacher Report noted that if the two-time Bundesliga winner joins United next season, a pairing of him and Chris Smalling will be effective due to Hummels' ability to play possession-based football. The possibility of the pairing was even compared to the legendary United defensive duo of Rio Ferdinand and Nemanja Vidic.

According to Transfermarkt, Hummels current value is at €35 million but Dortmund will probably ask for more. However, BVB CEO Hans-Joachim Watzke told Bild, as translated by talkSport, that the reported fallout between Hummels and Tuchel is not true.

"Today I read of a problematic relation between Mats and us. But that's definitely not true. Mats Hummels is a very important player for us. He is our captain. I have an excellent relationship with him," Watzke said.

"Sometimes he is not too easy, but that does not have to be a disadvantage. He is a very decent guy, and we will support him entirely. There is nothing more to say about it," he added.

Dortmund recently lost back-to-back games with Hummels, scoring an own goal in the defeat against Hamburg. He also conceded that decisive penalty in the first minute versus FK Krasnodar in the 1-0 loss in the Europa League match on Thursday. Even though he was at fault for the goal, Goal.com reported that he put a solid performance after committing the mistake.