Gareth Bale did not feature in Wales' defeat to Macedonia because of a groin strain, and has gone for a scan to determine whether he will be involved in Tuesday's meeting with Serbia.
Bale, the world's most expensive player following the completion of 100million euro move from Tottenham to Real Madrid, was an unused substitute when the Dragons slumped to a 2-1 loss in Skopje on Friday night.
Chris Coleman had insisted Bale was injured when questioned on his decision not to use him on Friday, but only revealed the problem on Monday.
He said: "We had a conversation with Gareth before the game, he had a tight groin from the day before and we could not take that chance.
"As we speak he has gone to have another scan on it to clear his mind so he knows everything is alright."
Bale has not played since mid-July due to a foot injury and his latest injury concern comes just a matter of days before he is scheduled to make his Madrid debut at Villarreal.
Coleman revealed the 24-year-old suffered the problem during Wales' training session at the Philip II Arena on Thursday, which he was not present at after losing his passport, on a playing surface which the Dragons' set-up were not particularly impressed with.
But Coleman is still hopeful the results of the scan will allow Bale to play some part against Serbia in Cardiff on Tuesday.
"We went into the Macedonia game with everything great," said Coleman.
"Gareth gets his move to Real Madrid, everything is positive.
"Then Gareth picks up a strain in training and can't play in the game which is disappointing."
He added: "He was never going to be available to start either of these games but at best he would have come on for maybe half an hour.
"There is a small chance of that tomorrow night, we will see when we get the scan results back and how he feels."