Mainoo's future at Old Trafford has been the subject of growing speculation in recent months and the latest reports suggest he could be at the centre of a huge transfer.
Back in January, it was reported that he would be willing to sell the youngster for the right price, sparking from supporters who see him as key for the future.
But under Ruben Amorim, Mainoo has struggled to cement a starting spot. With Bruno Fernandes, Casemiro and Manuel Ugarte ahead of him in the pecking order, his game time has been limited.
As a result, he even requested a loan move in the final days of the summer window that was turned down by the club. Mainoo remains under contract until 2027, although United do have the option to extend by a further 12 months.
But speculation over his future has continued and reports from Spain suggest Mainoo could be part of a swap deal to bring in Federico Valverde from Real Madrid.
According to Spanish publication Defensa Central, United are prepared to offer Mainoo plus £44m for the Uruguyan.
However, Valverde is regarded as a key figure in Xabi Alonso's plans and Real Madrid are expected to resist any approach. But the move itself appeals to Mainoo.
According to The Athletic, the midfielder would prefer a switch to the continent rather than another Premier League side. The Mail also reported that it was just not Real Madrid keeping tabs on him, with Atletico Madrid monitoring his situation.
Chelsea have also been linked with Mainoo's signature. After Alejandro Garnacho's transfer in the summer, the two clubs have shown they are willing to do business together, which could make negotiations easier.
Towards the end of the summer window, reports claimed United were open to offers of around £45m for Mainoo.
Given the talent he has already displayed, many felt that fee was too low in the current market. In his breakthrough campaign, Mainoo was the player of the match in the FA Cup final victory over Manchester City, before forcing his way into the England team for their run to the Euros final.
Last season proved more difficult, with injuries and Amorim's tactical demands limiting his minutes. He still showed flashes of his quality, most notably a composed late equaliser against Lyon.
The struggles have continued into this season. He has started just once, in the Carabao Cup defeat to Grimsby and has played just 76 minutes in the Premier League.
With no European football, or cup competitions until January, his route back into the side looks difficult.
Topics: Federico Valverde, Football, Kobbie Mainoo, Manchester United, Premier League, Real Madrid, Ruben Amorim, Transfer News
