The Reds have it all to do in Thursday's last 16, second leg match against the Spanish side after a 3-2 defeat at Old Trafford last week.
Both English and Spanish press and photographers were invited to watch the first 15 minutes of the session, with a total of 20 players put through their paces by the coaching staff on a warm evening in Bilbao.
Antonio Valencia looked sharp having recovered from a hamstring strain, while Chris Smalling also took part in the session after he was forced off in the first leg thanks to the head injury sustained on international duty. Sir Alex did however reveal, at his pre-match press conference, that the England defender is probably only fit enough for a place on the bench.
Club photographers John and Matt Peters, as well as fellow snappers from Getty Images, were on hand to capture the players in action for our gallery above.