Chris Coleman has not given up hope that Gareth Bale will declare himself fit to feature at some stage against Serbia on Tuesday night but the Wales manager has warned Real Madrid that it would represent a "big gamble" to start the world's most expensive footballer against Villarreal on Saturday.

Bale injured his groin in training on Thursday, before Wales's 2-1 World Cup defeat in Macedonia the following evening, when Coleman named the 24-year-old on the substitutes' bench but had no intention of using him. Although Bale trained with the Wales squad on Sunday, Coleman revealed that the forward requested a scan on his groin on Monday "just to clear his mind so he knows he is all right", before playing a full part in a closed session at Cardiff City Stadium.

Coleman said he was under no pressure from Madrid to leave the £86m player on the sidelines and that it would be down to Bale to decide whether he feels up to making his first appearance since a pre-season friendly for Tottenham Hotspur against Swindon on 16 July.

The Wales manager made it clear that Bale "is never going to be available to start" in the World Cup qualifier and suggested that Madrid should tread carefully when it comes to Saturday's La Liga fixture.

Bale, according to Coleman, has completed only four training sessions in the past eight weeks and one of those was a one-on-one workout with the Wales physio, Sean Connelly, before the friendly against the Republic of Ireland last month, when the player was struggling with a foot problem. Although Bale has recovered from that injury, he complained to Coleman that his groin was causing him discomfort on the morning of the Macedonia match.

"There's a picture of him [in training on Thursday] and, as he kicks the ball, the turf comes away, his ankle rolls and he gets a bit of a strain with his groin," Coleman said. "He continues with the session, wakes up in the morning and it's tight and I can see what he's thinking. If he had had 10 games building up to it, it wouldn't have been in his head. But he hasn't had anything.

"And he's thinking if he starts, or if he comes on, and that turns into something bigger, it doesn't look good for him first and foremost. Friday morning before the game he told me he wasn't ready. I wouldn't push anybody to take that chance. Saying that, if he comes back [from the scan] and says he's feeling better, it's not even an issue.

"If Gareth says to me he can play a part, then he is coming on to the pitch. I have to take Gareth's word. He always turns up for Wales – if he didn't want to be here, then he wouldn't be here. God knows he's got excuses not to be."

Asked whether he believed Bale would be ready to start for Madrid against Villarreal, Coleman said: "I don't know. Physically it's a big gamble. Especially if he plays some part for us and then he has to travel back. As a manager you would never dream of going back into pre-season having four sessions and organising a friendly, even a pre-season one, never mind an international qualifier after that many sessions.

"La Liga is a different tempo to the Premier League but I'd be surprised if he starts. I understand they've got a problem with Cristiano Ronaldo but it's a big, big ask to do four sessions [and then play]. Gareth's a super athlete, he's not got an ounce of fat on him but even him, if you see him in the sessions with us – and we're not full pelt – he's not quite there. It will be up to him. If he says he can play a part [for Real Madrid], he'll be on the pitch no doubt."

With or without Bale, Coleman will be picking from a threadbare squad for a game that Wales have to win to have any chance of achieving the third-place finish the manager has targeted to give them a higher seeding and, in turn, a potentially easier draw for the 2016 European Championship.

Ashley Williams is suspended, Jonathan Williams faces six weeks out after damaging knee ligaments in Macedonia and Sam Ricketts is doubtful with a knee problem.

The absence of Ashley Williams means that Aaron Ramsey could be given the captaincy for the first time since the 6-1 defeat in Serbia 12 months ago.

"I always believed one day Aaron would be the captain again. I think he just had to concentrate on his own game and he's done that," Coleman said.

"He's been brilliant with Arsenal, he comes with us and he runs the game. From where he was last year to now, mentally he's in a different place."

Wales (4-2-3-1, probable): Myhill; Matthews, Gabbidon, Davies, Gunter; Vaughan, Ledley; Collison, Ramsey, Robson-Kanu; Bellamy.

Serbia (4-5-1, probable) Stojkovic; Ivanovic, Bisevac, Nastasic, Kolarov; Tadic, Duricic, Markovic, Fejsa, Radovanovic; Dordevic. Referee S Marciniak (Pol)

TV: Sky Sports 1, kick-off 7.45pm