The striker had to be substituted in the second half at Vicarage Road as the Gunners let the lead slip and ended up losing to the Hornets.
Welbeck has struggled with a string of injuries at Arsenal since his move to the club from Manchester United back in September 2014.
It now looks as though the 26-year-old will be out of action for a number of weeks after picking up a fresh muscular problem in Saturday’s game at Vicarage Road.
And Wenger revealed after the game that Welbeck had indeed suffered a suspected hamstring injury – although he doesn’t yet know how serious it is.
Speaking at his post-match news conference, Wenger said: “It looks to be a hamstring with Welbeck.
“I don’t really know because everybody is shocked in the dressing room [about the result]. It looks a muscular problem.”
Saturday’s defeat left Arsenal nine points behind leaders Manchester City in the Premier League table and with it all to do if they are to challenge for the title this season.
The Gunners will return to Premier League action next weekend with a trip to Goodison Park to take on Everton as they look to try and get back to winning ways in the top flight.
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