Crystal Palace's Joe Ledley will miss the FA Cup final and is rated "50-50" to be fit for Wales at Euro 2016.
Ledley fractured a leg against Stoke, but Wales assistant manager Osian Roberts has said he could be in their squad for France even if he is not fit.
"I think he's 50-50 [to make Euro 2016] - it's as tight as that," said Palace manager Alan Pardew.
"I'm sure Chris Coleman will be desperate to have him, so we're doing everything we can to help him."
Coleman names his 23-man squad for Euro 2016 on 31 May, and Wales play their first game on 11 June against Slovakia.
Ledley, 29, was named in Coleman's provisional squad for the tournament in France, before being ruled out of the FA Cup final.
Pardew described the loss of the midfielder for the match against Manchester United on 21 May as "desperate" news.
He said: "He was very disappointed when he heard the news but he's a strong character and now he's just determined to make the Euros, so he's got a good mindset again."
Pardew revealed the club will use an oxygen chamber to try to aid Ledley's recovery time.
Minor fractures can take up to six weeks to heal, though the recovery time for more severe fibula injuries can be about three months.
Roberts says Wales could take Ledley to Euro 2016 even if it means the former Cardiff player missing the early part of the competition.
"If he misses the opening game, but is available for the others, we'd want Joe to be part of things," said Roberts.
"If we need to give Joe a little bit of extra time, we'll do so. He deserves that.
"He's been a vital cog in the team for quite a few years and we hope he can recover in time.
"We'll have to wait and see how he reacts over the next couple of weeks. We're a stronger squad with Joe in it."
After facing Slovakia, Wales take on England in Lens on Thursday, 16 June before finishing the group stage against Russia on Monday, 20 June.
It would be a significant blow to Coleman if Ledley was missing from his Euro 2016 squad, as Wales prepare for their first major international football tournament since 1958.
He played an integral part in qualifying for France, featuring in seven of the 10 Group B games, and offers valuable experience to the Welsh midfield.
Wales will travel to Portugal for a pre-tournament training camp on 23 May.
After the final squad announcement, Wales play Sweden away on 5 June, their last friendly before Euro 2016.