Billy Davies admits Nottingham Forest are struggling to get to the bottom of Guy Moussi's ongoing ankle injury.
Moussi, who missed four months of last season with an ankle problem, has not featured in Forest's last five Championship matches and no timescale has been set for his return.
The midfielder has undergone scans on the injury and Forest boss Davies is hoping the problem will eventually clear up.
"He is still struggling with his ankle injury," Davies told the Nottingham Evening Post.
"We have had it X-rayed, we have had it scanned - we have done all that we can.
"But, unfortunately, he is still struggling. The scans and X-rays both came back clear. It is a bit of a mystery.
"I don't know what else we can do. Hopefully he will be back sooner rather than later.
"There is nothing too severe in there. We just have to hope that it rights itself quickly."