West Ham United have raised concerns over Manchester United's bid to sign Mateus Fernandes. According to reports, the Red Devils have yet to submit a formal offer for the 21-year-old, who has impressed in his debut season at the London Stadium. West Ham are adamant they don't have to sell and want £80 million for the player. Manchester United's willingness to meet this valuation is uncertain, with sources at West Ham being 'dubious' about the deal getting done. The Red Devils have already begun talks to sign Fernandes before the start of the new Premier League season, while Arsenal are also interested in a deal for the 21-year-old. West Ham face the prospect of selling several key players this summer, including Fernandes, Jarrod Bowen, and Crysencio Summerville. The club's valuation of Fernandes is £80 million, which is a significant amount considering the player's relatively short time at the club. West Ham signed Fernandes from Southampton last summer in a deal worth £38m plus £4m in add-ons. The Brazilian midfielder is still to undergo a medical, but Manchester United are confident the transfer can be finalised before Michael Carrick's side report back for pre-season training in July. Manchester United are also targeting Newcastle United left-back Lewis Hall, who is valued at £50m. The Red Devils have agreed a £35m deal with Atalanta to sign Ederson, a Brazilian midfielder who is expected to solve Manchester United's biggest problem in midfield.