Midfielder Gera picked up a knee injury at Loftus Road and Fortune, who came on to replace him, ended up having to be replaced himself due to a hamstring problem.
Gera was sidelined for six months last season with a knee injury but Albion are hoping this setback will not prove anywhere near as serious.
Baggies assistant boss Kevin Keen said: "Zolly had a problem with his knee. We'll have it scanned and go from there.
"We've all got our fingers crossed, knowing Zolly's history, that it's not too bad. Hopefully, he'll be back in a West Brom shirt pretty soon.
"But, until we see the scans and see specialists, we'll have to wait and see.
"Marc has got a little nick on his hamstring. Hopefully it's not too bad but, again, we will just have to wait and see."
West Brom were already without Jonas Olsson, Steven Reid, Claudio Yacob and Goran Popov due to injury, and Keen admits that plans to remain quiet during the transfer window may need a re-think.
"Perhaps we'll have to reassess," he said. "But, up until Saturday, we were quite happy with what we've got, as long as we didn't lose too many and there were no surprises.
"George Thorne has come in as a 20-year-old and done well. I think that, if we can promote players like that, it would be more in our favour.
"There are no imminent plans to make a marquee signing, that's for sure."