Manchester United have been linked with a move for Borussia Dortmund star Karim Adeyemi, amid reports that the winger has fallen out with his current manager Niko Kovac. The 23-year-old's entourage are seeking to negotiate a long-term contract extension with the German club, with Adeyemi's deal set to expire in 2027. However, a stand off is expected, as the player is demanding a release clause. Speculation over Adeyemi's future has ramped up in the past few weeks. Bild reports that negotiations between Borussia Dortmund and the player's representatives have taken place, with his agent Jorge Mendes demanding a release clause of £70 million be included in a potential extension. The German giants typically do not include release clauses in their contract, however, the report by the outlet suggests an exception could be made in this instance. Mendes enjoys a fruitful working agreement with the Red Devils, and it is understood that they have been alerted to the 23-year-old's displeasure with his manager. The Portuguese super agent has facilitated switches to Old Trafford for his clients Leny Yoro and Manuel Ugarte in the past few years. Adeyemi has cut a frustrated figure in the past few weeks, prompting a public response from Kovac. After a promising start to the season, the mercurial youngster has gone through a barren spell. He has failed to score or log an assist since late September. During BVB's 1-0 victory over Köln last month, the winger threw a water bottle at the bench after he was subbed. Kovac publicly lambasted his star's behaviour. The ex-Croatia and Bayern Munich manager said: "I think that's unnecessary. It's okay that he can be angry sometimes, but that's unnecessary, he's an adult." Their relationship took another dramatic turn on the weekend during Dortmund's 1-1 draw with Hamburg. Kovac cut a frustrated figure on the sidelines, visibly remonstrating at Adeyemi after the winger made some poor decisions in the final third. The pair argued on the bench after Adeyemi's 66th minute substitution.Looking for smarter football bets? Get expert previews, data-driven predictions & winning insights with GOAL Tips on Telegram. Join our growing community now!Despite the apparent breakdown in their relationship, Kovac has continued to pick Adeyemi from the start. The German international had a frustrating evening in Dortmund's 4-1 loss to Manchester City in the Champions League last week, as he missed a couple of chances. His manager again removed him from the fray, this time in the 81st minute. Kovac gave his star a pat on the back as he was replaced, before protecting the player in his post-match press conference. When asked about his decision and the rumours of a fractious relationship between the two, Kovac said: "That’s an internal matter."We have a special relationship. Offensively, he played a good game. He needs to reward himself for his play more often because he had two or three really good chances. Note that, at the other end [Manchester City’s] Phil Foden converted similar chances. I wish he could have done the same, but he didn’t."Despite his disappointing run of form, Adeyemi is a highly rated player that could bolster most teams' attacking stocks. He has scored 29 goals and provided 22 assists in 121 games for the Bundesliga side since joining from Red Bull Salzburg in 2022. His potential has seen him make the occasional appearance for Die Mannschaft; he has won 11 caps and scored one goal for the senior German national side since making his debut in 2021. His recent appointment of Mendes as his agent could certainly facilitate a switch to Old Trafford, but an improved deal with the Black and Yellow cannot be ruled out either. However, with Nico Schlotterbeck also rumoured to be displeased with Kovac's management seeing the centre back being linked with Liverpool and Bayern, the senior executives at Signal Iduna Park might be facing an uphill battle to keep hold of their disgruntled players. It will be interesting to see if these reports affect the manager's starting lineup when Dortmund face Stuttgart following the international break.