The Arsenal star had just seen his team-mate go to ground in a sickening moment where Welbeck’s ankle twisted at right angles.
As Henrikh Mkhitaryan rushed to help, Guendouzi’s face was a picture of shock.
The 19-year-old Frenchman put his hands to his head in horror as to what he had seen – as medics rushed on to help.
Welbeck was given oxygen on the pitch and there are now fears the injury could be ‘career-ending’.
Medical expert Johnny Wilson, who holds multiple degrees in sports medicine and has worked for three professional football clubs, provided a devastating verdict on the potential severity of the injury the England international suffered.
“Injury to #Welbeck. Possible fracture dislocation of ankle which could [be] career ending,” Wilson wrote on Twitter.
“Structures within the ankle which could [be] injured [are] the medial, lateral, anterior & posterior ligaments, tibia, fibula & talus bones as well as chondral surfaces. Will need [to be] imaged #AFC.”
Wilson then went into detail on the specific tests Arsenal doctors will conduct to assess Welbeck’s injury.
“X-ray will [be] used as 1st line of imaging [to] assess integrity of bones: tibia, fibula, talus, calcaneous & other smaller bones in foot especially – 5th [metatarsal]!” Wilson added.
“He will also [have an] MRI within next 24-48 hrs [to] assess soft tissue structures such as ligaments muscles tendons & chondral surface.”
Unai Emery admitted the injury suffered by Danny Welbeck during Arsenal’s goalless draw with Sporting Lisbon had an adverse effect on his players.
Emery, whose side extended their unbeaten run to 15 games by shutting out Sporting, conceded the situation weighed heavy on his players.
“It’s the worst news tonight, this injury. It’s clear that we are with him in these minutes,” he said.
“He was working well and he was having a good match. He had some chances too. His injury was with the mentality of the players. They saw it was a big injury.
“When you are playing football, when you are playing in competitive matches, it can happen. You don’t want it to happen but this is our profession.
“Now he is at the hospital. The news is that we are going to wait – but we think it’s a serious injury.”
Welbeck has endured a number of serious injuries during his career and it remains to be seen how long his latest setback will leave him on the sidelines.
The 27-year-old is out of contract at the end of the season and Emery would not be drawn on whether Welbeck’s future is at Arsenal.
“He’s a very good person,” he said.
“His commitment with us is very big. He’s helped us with his behaviour, with his quality and his capacity.
“It’s a very big injury for him, for us, for all people who like and love him as a person.”