Barcelona have made United States youth international Konrad de la Fuente an ultimatum, sources have told ESPN, as negotiations continue over a new contract.

The Spanish club have made De la Fuente an improved offer, with his terms up in the summer, but have told him if he doesn't accept it he risks being sidelined for the rest of the season.

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ESPN revealed last month that talks over a contract renewal had stalled with De la Fuente keen to move to Hertha Berlin, where he would link up with former U.S national team coach Jurgen Klinsmann.

There has also interest from other Bundesliga clubs.

Barca remain keen to hang on to the forward and have upped their offer to an initial salary of €450,000 annually rising to €600,000 over the course of a three-year deal, club sources said.

However, the latest offer comes with an ultimatum: sign the terms or risk not playing for the club again.

De la Fuente, 18, would initially play for Barca B in the Spanish third division, with a plan in place to eventually progress to the first team. He is playing for the U19s and made his first appearance of 2020 on Sunday following an injury, scoring after coming on as a substitute against Atletico Villacarlos.

The Miami-born forward has not yet responded to Barca's offer, with sources close to the player explaining the allure of playing top-level football in Germany is appealing to him.

He has been at Barcelona since 2014, though, and is grateful for everything the club have done for him so far.

Barca are aware of the interest from German sides but sources say they've received no bids for the player is this month.

De la Fuente will be free to leave in June if he doesn't renew, although any club would have to pay Barca development rights of up to €700,000.

De la Fuente, whose parents are from Haiti, is a regular with the U.S. U20s.

In an interview with ESPN last year, he described himself as a "dynamic winger, who is fast, skillful, tricky and likes to take players on."