The Belgian midfielder limped off half an hour into Tuesday's 0-0 draw at Scunthorpe with a calf strain.
He has played in the Saddlers' past 11 games, his longest run since his second spell on loan with Walsall in 2012.
"He's been so unlucky with injuries. But you're always at your most vulnerable when you're at your best," Walsall boss Jon Whitney told BBC WM.
"He's really down. It's a kick in the teeth but I'll help him get over it.
"We haven't had a chance to bring him over, as he lives in Sheffield, and we're trying to get him scanned to know what we're dealing with.
"It's still non-weight bearing," added the former Saddlers physio. "He's still on crutches. We'll know more by Monday. He got his studs caught in the grass. But, from the pain he's in, it's not going to be a short-term injury.
Cuvelier's run of fitness has coincided with Walsall's best run of results this season - a sequence of just two defeats in 11 games, which has lifted them to 12th in League One.
The first game which the influential Cuvelier will miss is Saturday's visit of Peterborough, when Amadou Bakayoko hopes to start, after being replaced in midweek by Simeon Jackson, along with Franck Moussa and Andreas Makris.
Reece Flanagan remains out with a dislocated shoulder which, on top of a serious knee injury, is expected to keep him out for the rest of the season.
Jon Whitney was talking to BBC WM's Rob Gurney
Walsall boss Jon Whitney says he is awaiting news on the full extent of Florent Cuvelier's latest injury.