The England forward landed awkwardly as he challenged Bruno Gaspar for a header early in the first half, with his team-mates showing immediate concern for his plight.
"The worst news tonight is these injuries", the Spaniard told a media conference.
"The objective is for him to come back to us and grow up with us after this experience".
It was the hosts that took the game to their opponents, and they were lucky to still be on level terms before half-time.
He has scored five goals in six Bundesliga appearances and impressed in two appearances in the Champions League. "We don't want it, but this is our profession".
Welbeck collapsed in pain after a collision in the Sporting penalty area 25 minutes into the game at the Emirates and immediately waved for medical attention as he writhed on the ground.
Rangers are now level on points with Spartak in an incredibly tight Group G, one point behind leaders Villarreal after the Spaniards´ goalless draw with Rapid Vienna in Austria. They saw it was a big injury. You can also stream the match via B/R Live and Univision NOW.
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.
The home side started positively enough with Matteo Guendouzi getting in behind the visitors backline to send a low ball in, but Welbeck's flick was hacked off the line.