The recent recruit started for the first time since joining the Reds, appearing in midfield ahead of James Garner and Donny van de Beek, in the 1-1 draw with the Spanish side.
The competitive action gets under way next weekend, on the same stage, with Brighton & Hove Albion providing the opposition, and the new no.14 is confident Erik ten Hag's team can make a good start in the Premier League, ahead of a reunion with his former club Brentford in our opening away fixture.
"It was very different, also when walking into the stadium," he said of his first appearance at home as a United player.