The Arsenal forward was challenging Sporting full-back Bruno Gaspar for a header when their legs tangled and Welbeck landed awkwardly on his ankle.
"The worst news tonight is these injuries", the Spaniard told a media conference. We wish him all the best in his recovery.
The game only really opened up in the 88th minute when Jeremy Mathieu was shown a straight red for a foul on Pierre-Emerick Aubameyang as the striker raced through on goal.
The Londoners moved six points clear of Hungarians Vidi at the top of the group and have not tasted defeat in 17 matches since losing the Community Shield to Manchester City in August.
Oil tanker & Norwegian Navy frigate ‘collide’ off country’s coast, 7 reported injured
The warship is now in danger of sinking, while the tanker, named the Sola TS , is slightly damaged and did not spill oil. The shipping site Sysla reported that the tanker had been loaded with crude oil and was on its way to the UK.
However, they have not lost since, are fifth in the Premier League, have won all three of their Europa League games and are into the quarter-finals of the Carabao Cup. You can also stream the match via B/R Live and Univision NOW.
But it was Welbeck's injury just before the half hour mark that was the main talking point from a largely forgettable Emirates Stadium encounter. They saw it was a big injury.
Elsewhere, Eintracht Frankfurt reached the last 32 with their fourth win from as many group games by beating Apollon Limassol 3-2 in Cyprus, while Lazio joined them in progressing from Group H as goals from Marco Parolo and Joaquin Correa secured a 2-1 win over Marseille to eliminate last season´s runners-up.
This latest setback comes on the day he was named in Gareth Southgate's latest England squad for the forthcoming games against the United States and Croatia.