Having trained alone since Wales arrived in Qatar, Allen joined the rest of the squad for Wednesday's session.

On Thursday, boss Page said: "We've got a decision to make on that - what's best for the team."

However, the Wales boss is also pondering the effects of playing in the heat of Qatar, saying: "We've got a few tired bodies, a few go down with cramp."

On Allen, Page added: "The medical team have been exceptional and they're the reason he's now fit.

"We were all concerned about him, the way he kept breaking down. He's had to meet targets along the way, he's met every one. If we'd played him in game one and he'd broken down he would have been completely out.

"We could have pushed him for USA, but due to the confidence we have to get out of the group I want him for the long-term."

Wales started their first World Cup campaign for 64 years with a 1-1 draw against the United States on Monday and face Iran in their second Group B game on Friday.

Allen's ability to play some part against Iran is a major boost for Wales.

He was missed during the first half against the USA, when Wales were overrun in midfield and fortunate not to trail by more than the 1-0 half-time deficit.

Wales captain Gareth Bale said: "Joe is a massive player for us and doesn't get credit he deserved - he's a vital cog in the way we play.

"To have him available is a massive boost for us with two games remaining so hopefully he can come on or start and he'll do what Joe Allen does best and cover every blade of grass.

"I think he's shown time and again how important he is and we hope he has a few miles left to go."

Wales could take a significant stride towards qualifying for the knockout stage with victory against Iran, who were thrashed 6-2 by England in their first match.