Crystal Palace are growing frustrated with Manchester United as talks continue over the signing of Aaron Wan-Bissaka, sources have told ESPN FC.

United have seen two bids for the defender, who scored an own goal for England's Under-21s during their 2-1 defeat to France on Tuesday, rejected because Palace are seeking more cash up front.

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The two offers, according to sources, have centred around a structured payment plan and a series of add-on clauses to push the proposed deal close to Wan-Bissaka's valuation of between £50 million and £60m.

Palace are prepared to let the 21-year-old leave but want a larger proportion of the fee to be guaranteed.

United are expected to return for a third time with an improved offer. Wan-Bissaka is Ole Gunnar Solskjaer's top target at right-back as he looks to bolster his defence.

The Norwegian is also keen to sign a centre-back after United conceded 54 league goals last season with Leicester's Harry Maguire among the options.

Solskjaer has already secured the signing of £15m winger Dan James from Swansea and, after bringing in defensive reinforcements, is set to turn his attention to strengthening his midfield.

Solskjaer wants at least one midfielder ahead of next season after Ander Herrera opted to leave the club on a free transfer. Newcastle's Sean Longstaff, Sporting Lisbon's Bruno Fernandes, Monaco's Youri Tielemans and Atletico Madrid's Saul Niguez are all on the list of targets.

Solskjaer's transfer window has complicated by the potential departures of Paul Pogba and Romelu Lukaku.

The United manager was keen to keep both at Old Trafford this summer but Pogba has publicly declared he wants a "new challenge" amid interest from Real Madrid and Juventus while sources have told ESPN FC that Lukaku wants to move to Inter Milan to link up with Antonio Conte after falling behind Marcus Rashford in the pecking order at United.