Barco posted an emotional farewell on Instagram on Monday evening, making clear he would not be returning to the club that transformed his career.
"Today I say goodbye to this club. I always left everything on the field at every game for this shirt.
"I want to thank my teammates who made everything easier for me, Liam and his staff for the confidence they gave me and for making me the player I am, Gary and his staff for understanding me and helping me improve, to everyone who works at the club and supports us every day, and to the fans for the love they always gave me.
"From afar I will continue to support and encourage you. Thank you very much for this year and a half, and many successes for the future. Thank you, Strasbourg."
Barco, who joined Strasbourg from Brighton & Hove Albion for £7.9m in January 2025, was initially deployed as a left-back before head coach Liam Rosenior converted him into a central midfielder — a change that produced an outstanding run of form. He contributed three goals and nine assists across 43 appearances in all competitions this season, drawing comparison with some of the best young midfielders in Ligue 1 and earning a recall to the Argentina squad.
According to journalist Ben Jacobs, Chelsea are expected to make the signing official next week following the end of the Premier League season. Argentine journalist Gastón Edul confirmed the deal is done, writing that there is a contractual agreement in place with the player and an understanding between the clubs. The fee has not been officially disclosed.
He would become the fifth arrival at Stamford Bridge from Strasbourg this summer, following striker Emanuel Emegha, winger Geovany Quenda, forward Dastan Satpaev and defender Denner. Chelsea have now conducted 13 deals with Strasbourg since the start of last season under shared BlueCo ownership.
Barco is understood to have signed a six-year contract. He may operate as a squad option or left wing-back under incoming manager Xabi Alonso, who officially takes charge on July 1.