Crystal Palace boss Roy Hodgson has confirmed Nathan Ferguson has suffered a setback in his return to fitness.
The 20-year-old has yet to play for Palace following his summer move from West Brom as he arrived with a knee injury.
He had returned to full training ahead of Sunday's clash with Tottenham but has now suffered a thigh injury, with an MRI scan required to find out the full extent.
Hodgson said: "It is quite sad news. He was and is getting on very well and actually joined in with us this week and has just become a bona fide member of the squad without us having to moderate what he can and can't do.
"But unfortunately as sometimes happens in these situations, especially as he is young and enthusiastic, it has led to him picking up a slight thigh strain. At the moment I am waiting on the results of that thigh strain from the MRI. It is very unfortunate.
"The good news is that it has got nothing to do with the knee injury. It was good that he came through the training so well with his knee but no doubt his enthusiasm in stepping up in the intensity of his training has provoked a thigh strain.
"He trained on Thursday, it was only when I arrived on Friday and spoke to the doctor that they informed me that he wouldn't train because of this feeling in his thigh.
"They told me they were going to get it scanned and we'll wait and see. I have no idea (how bad it is) and they weren't prepared to get involved in any guesswork."
Palace, who got back to winning ways at West Brom last week after a run of defeats, are entering a crucial period as 12 players are out of contract in the summer.
Christian Benteke, Andros Townsend and Patrick Van Aanholt are among those who could leave on a free, but Hodgson wants to keep his squad together.
"I'm not desperate for that change. I've been working with many of them for a long time, and I appreciate what they can do," he said.
"Of course our squad is a big one and a lot of players in the same position where only one or two can play, that doesn't exactly make it easy for them or myself.
"But the bottom line is, players who have contracts running out will have decisions to make, and the club will as well.
"I certainly am not looking to lose people.
"There's a lot of games coming up for a team like us. That will open up opportunities for players to get a look in."
