Wales seem set to be without captain Craig Bellamy for the friendly in Montenegro on Wednesday.
The Manchester City striker did not appear at Cardiff Airport for Monday morning's flight to Podgorica.
So far the Wales management has not received any communication from either the player or his club to explain Bellamy's absence.
Midfielder Joe Ledley has been passed fit to travel after illness, but Dave Edwards is out with a groin injury.
A Football Association of Wales spokesman confirmed that they were unsure why Bellamy had not joined up with the squad: "The player and club were notified about the game some while ago, but last night we had not heard from either the player or the club.
"The same applies to this morning, we just hope the player is all right."
Manchester City manager Mark Hughes, the former Wales boss, hinted before the weekend that Bellamy has a knee problem.
Bellamy did not figure in Manchester City's pre-season friendly against Rangers last Wednesday and Hughes said they are monitoring the player's ongoing knee problems.
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"With his past history of knee injuries, we are trying to protect him," said Hughes.
"We are very cautious about letting him play three games in a week, which is why we left him out of the Rangers match on Wednesday.
"He still gets discomfort from the injury, so he will speak to the Wales manager [John Toshack] and I would suggest he will not be available for Wednesday.
"For qualifiers it is not a problem but friendlies are different and I expect the situation will be dealt with accordingly."
Ledley has been suffering from illness all week and had to be withdrawn at half-time of Cardiff City's opening day 4-0 win over Scunthorpe.
But the 22-year-old reported for duty at Wales' Cardiff base on Sunday night.
Wolves player Edwards, 23, was assessed by the Wales medical staff and was ruled out of the trip.
His fellow midfielder Carl Fletcher, 29, is also a withdrawal after the Plymouth Argyle player called Wales manager John Toshack to say he was retiring from the international game, having won 36 caps for his country.
Wales have a clutch of talented young midfielders developing and it it thought that Fletcher has opted to step aside for the future generation.
Tottenham full-back Gareth Bale and Fulham midfielder Simon Davies were already out of the trip to Podgorica.
But West Ham defender Danny Gabbidon is included in the 22-man Wales squad following an injury-ravaged 18 months.
The 29-year-old has suffered a complicated abdominal problem, but is continuing his rehabilitation from his injury nightmare.
There was also an injury blow for the Wales Under-21 side ahead of their Uefa Under-21 Championship qualifying clash against Hungary at Wrexham's Racecourse Ground, also on Wednesday.
Swansea City midfielder Joe Allen limped out of their opening day loss away to Leicester City on Saturday with a hamstring injury and will miss out, while Chelsea have withdrawn goalkeeper Rhys Taylor.
Wales Under-21 manager Brian Flynn has called-up Swansea's David Cornell, the Under-17s goalkeeper, as well as Cardiff defender Adam Matthews, who has been capped by the Under-19s.
