Atletico Madrid’s Juanfran will miss both matches against Arsenal, handing the Gunners a boost ahead of the tie.
The 33-year-old defender has started every one of Atletico’s Europa League games this season but will miss the next two-to=-three weeks with a hamstring injury that he picked up in their goalless draw with Real Betis at the weekend.
He has two goals in six appearances in the competition.
Juanfran had to be replaced after 65 minutes with a recurrence of a problem that has dogged him all season.
Sime Vrsaljko, 26, who replaced Juanfran on Sunday, is expected to take his place.
Arsenal, meanwhile, will be without Mohamed Elneny who will miss the next few weeks with ligament damage to his ankle. It had been feared he would miss the World Cup which would have been a real shame for the Egyptian, but Arsenal hope to have him back before the season comes to an end.
Henrikh Mkhitaryan will also miss the first leg as he returns cautiously from his knee problem. The midfielder has been undertaking light training.
Mesut Ozil, who had ‘flu once again just before a big match, should be fit to return.
Jack Wilshere has also returned to training and is expected to be fit for Thursday.