Barcelona are hopeful of making Junior Firpo their fourth signing of the summer this week following renewed negotiations with Real Betis, multiple sources have confirmed to ESPN FC.

The Catalan club want the deal completed before they fly to the United States on Monday and are increasingly confident of reaching an agreement with Betis over the left-back.

Betis are prepared to sell Junior for €25 million -- his release clause is €40m -- but Barca have not yet offered more than €20m.

If he signs, Junior, who turns 23 in August, would follow Frenkie de Jong, Antoine Griezmann and Neto in the door at Camp Nou during the current transfer window.

Barca coach Ernesto Valverde confirmed last week that the Spanish champions are in the market for a left-back. Jordi Alba was the only left-sided full-back in the squad last season and the club believe he needs competition for his place.

Valverde has been pushing for Junior and sources at the Catalan club say they are now optimistic of getting a deal over the line, although they're working on other options just in case, too.

The idea is to have a new left-back in as soon as possible with the new season less than three weeks away. Before then, Barca face Arsenal in the Joan Gamper Trophy on Sunday and then fly to the U.S, where they will face Napoli twice in the inaugural La Liga-Serie A Cup.

David Alaba was Barca's first choice due to his versatility and experience, but sources at the club have begun to admit defeat in their battle to get Bayern Munich to sell. "It's really complicated," one source said, due to Bayern's desire to keep the Austrian international.

Augsburg's Philipp Max is another target. The German has impressed technical director Eric Abidal and his assistant Ramon Planes, but the club have decided to heed Valverde's petition and move for Spain U21 international Junior.

The option of signing Manchester United's Matteo Darmian has also been explored. The Italian would represent a low-cost alternative to Junior and Max but Barca will only look to move for him if they fail to land their preferred targets.