Erik ten Hag's side meet the Spanish outfit at Old Trafford in Group E of the competition, with the home clash kicking off at 20:00 BST on Thursday night.
Martinez was withdrawn during the excellent 3-1 win over Arsenal at the weekend and was flagged in some quarters as a possible injury doubt but the signs certainly look positive for the Argentina international being available.
Anthony Martial was still missing from the group, as Ten Hag had indicated in his pre-match press conference when ruling the France forward out of the Old Trafford encounter.
Luke Shaw and Donny van de Beek, who were absentees from the matchday squad on Sunday, were also not spotted as our cameras filmed the session at our training base.