Troy Parrott has emerged as an injury concern for the Republic of Ireland after sustaining an ankle problem while playing for Millwall.
Parrott's competitive Millwall debut ended early as he was hooked at half-time during the Lions' Carabao Cup defeat by Burnley.
The Republic face Slovakia in their Euros play-off semi-final in Bratislava on 8 October.
"It doesn't look great but we'll see," explained Millwall manager Gary Rowett.
"Troy got a kick on the ankle early on and he is a young lad, desperate to play and he has been devastated to be injured because he wants to play games," added the Millwall boss.
"You could see he was struggling movement-wise. He probably should have come off (earlier) or I probably should have taken him off.
"Obviously it's a big blow for us because we haven't scored as many goals as we'd like anyway and Troy was brought in to give us that extra quality, but at the moment he hasn't really been available."
In August, Parrott, who is on loan at Millwall from Tottenham Hotspur, was forced to withdraw from the Republic's squad for the Nations League games against Bulgaria and Finland with a quad injury sustained during pre-season.
The Dubliner, who made his international debut against New Zealand in 2019, starred for Republic boss Stephen Kenny during the pair's time with the under-21s.
'Hopefully not too serious'
While Rowett praised Parrott's work-rate and honesty, he warned the young forward against playing through the pain barrier in the future at the risk of aggravating an injury.
"He's such an honest kid, who is desperate to score goals and do well for us.
"And he's fitted in brilliantly with the group and worked incredibly hard, so it is more frustration from his point of view.
"Even when he's struggling he wants to stay out there, so everything he is doing is for the right reasons, but he has probably got to learn if he makes the injury worse, he will be out for longer.
"He is a bright lad and it is disappointing so far we've not really had him available, but hopefully it is not too serious and he will be available soon."