The 19-year-old defender was a starter in the friendly against Birmingham City and again in both of Saturday's matches in Italy, in a triangular tournament against Udinese and Nottingham Forest, and was among Barcelona's standout performers across all three games.
"Both in the match against Birmingham and in training he has made it clear to us that he is a top-level player," Flick said of him.
The German coach already knew the Catalan well before this summer, having promoted him to the first-team fold last season, when Espart featured in six matches across the Champions League and LaLiga. What has changed since is the consistency: Espart has started all three of Barcelona's exhibition matches during this pre-season and shown a growing understanding on the right flank alongside Karim Adeyemi.
Espart joined Barcelona's academy in 2015 as a young boy from UE Vilassar de Mar, and settled into the full-back position during his Juvenil years having previously played in midfield. It is that positional versatility, combined with his composure on the ball, that has stood out to the coaching staff.
Defensively, Espart is noted for his aggression and assurance in duels, along with his calmness, pace and positioning. Going forward, he offers the ability to carry the ball forward, combine with wide players, occupy space and stretch play, attributes that have made him difficult to leave out of Flick's pre-season plans.
Many of the academy players training with the first team this summer face uncertain long-term futures at the club, but Espart is not among the doubts.
He is under contract until 2028 and has made clear he wants to build his career at Barcelona, with Flick understood to be monitoring his progress closely as the club weighs up a new deal to protect one of its brightest young prospects.
The teenager reportedly gave up part of his summer holidays after a strong showing at the European Under-19 Championship to report early for pre-season, a decision that further impressed the coaching staff about his professionalism.
He has represented Spain at both Under-17 and Under-19 level, and his form this summer has him on course to be part of Flick's plans once the domestic campaign gets under way, alongside fellow academy product Héctor Fort.