Welbeck was taken to hospital during the second half of the game for an x-ray.
The medical staff then administered oxygen and applied a brace on his right leg before he was taken off on a stretcher.
Understandably, fans have been expressing their disappointment that Welbeck appears to have suffered yet another serious injury as his career at Arsenal has been blighted by a number of injury problems since he joined from Manchester United.
Welbeck has already suffered two long-term knee injuries since joining Arsenal in 2014, missing a majority of the 2015-16 and 2016-17 seasons. "He had some chances too".
"His commitment with us is very big". They saw it was a big injury.
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"The objective is for him to come back to us and grow up with us after this experience. We don't want it, but this is our profession".
Welbeck, who scored the winning goal in the reverse fixture in Portugal, was replaced by Pierre-Emerick Aubameyang in the 29th minute of the game.
Some of his team-mates were also visibly affected by the incident.
"The point isn't enough for us but at the moment our target is to be first in this group", he said.
He added: "Our mind is to be first in the group. We are following him every match and know he will help us in the future".
"We were aware of the opponent's quality but we, knowing our capacity and being creative and aggressive with and without ball, could try to surprise here".