The Gunners are in Italy, rather than Portugal, for the last-32 meeting.
“Thomas didn’t travel,” manager Mikel Arteta said on Wednesday. “He is not there yet. He is still training individually. Kieran (Tierney) has had one session with us and he is part of the squad.”
“It is very unusual,” Arteta said of the dynamic of a tie with two neutral venues.
“But as much as we can we have to try and maintain the integrity of the competition and the only way to do that at the moment is to play in different venues but at least play it over two legs and with away goals, as well.”
Why is Benfica vs Arsenal in Rome?
The tie has had to be switched to a neutral venue after the UK government’s decision to place Portugal on a red list of countries affected by new coronavirus variants.
That meant the game, originally scheduled to take place at the Estadio da Luz in Lisbon, had to be moved with Stadio Olimpico in Rome chosen.
Where is the second leg?
The second leg will take place at the Georgios Karaiskakis Stadium in Athens on 25 February.
The game, which was due to be held at the Emirates Stadium, was moved with government regulations meaning those arriving from any red-list country must self-isolate for 10 days, with no exemptions for elite athletes.