The Robins medical team have since diagnosed the problem as back spasm but it remains to be seen exactly how long the 22-year-old, who had initially hoped to return against Doncaster this weekend, will be out for.
"We know what the problem is and we know how to treat it," manager Gary Johnson told the Bristol Evening Post. "But we are not sure how hard we can push Evander and how soon.
"It's a difficult one. We need to work him hard in training to get him properly fit for the Championship but if we give him too much too soon we run the risk of him breaking down and returning to square one.
"He has seen a couple of specialists over the course of the last few weeks but there has been little change in his condition and it's becoming a concern."