Manchester United are growing concerned that David De Gea might have played his last game for the club, sources have told ESPN.

United chiefs believed they were close to an agreement with the goalkeeper to extend his contract but talks have dragged on and there are fears he could now leave this summer.

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Sources have told ESPN that the club decided against triggering a one-year extension to De Gea's contract, which would have kept him at the club until 2024. The option expired in May.

Instead, negotiations have taken place about a longer deal on a lower basic wage but including significant performance-related bonuses.

Sources have told ESPN that talks with De Gea are ongoing but that United are not as optimistic about reaching a compromise as they were a month ago.

De Gea, 32, has spent 12 seasons at Old Trafford and made more than 500 appearances.

Sources have told ESPN that earlier this season he was exploring the possibility of returning to Spain while there has also been tentative interest from clubs in Saudi Arabia.

United, meanwhile, are set to make a second bid for Chelsea midfielder Mason Mount.

A first offer of another £40 million ($51m) was immediately rejected by Chelsea, who want closer to £70m. United won't stretch that far but, according to sources, are hoping to agree a fee of around £50m.

Mount will enter the last year of his contract at Stamford Bridge this summer and there is little hope he will agree fresh terms.

The market for the Mount, which at one stage included Liverpool, Arsenal and Bayern Munich, has cooled significantly over the second half of the season and United are seen as the clear frontrunners for his signature.

United are hopeful that Chelsea's need to sell a number of players this summer will help negotiations move quickly to allow the possibility that Mount could be part of the squad ahead of the preseason tour of the United States, which starts in New York on July 20.