Santi Cazorla took part in a light training session prior to kickoff in Arsenal's Europa League semi-final first leg against Atletico Madrid.
The Spaniard has been sidelined since October 2016 after suffering an Achilles problem which forced him to undergo 10 operations and a skin graft amid fears that he might never play again.
However, Cazorla was put through his paces at the Emirates Stadium by Arsenal head of performance Shad Forsythe, performing several drills on the pitch.
The 33-year-old's Gunners contract expires at the end of the season but Arsene Wenger has previously expressed hopes of being able to offer the player a new deal, depending on his fitness.
Cazorla's last appearance for Arsenal came in October 2016 when Wenger's charges beat Ludogorets Razgrad 6-0 in a Champions League group-stage match.