Liverpool goalkeeper Caoimhin Kelleher has been denied a senior Republic of Ireland debut in Wednesday night's World Cup qualifier in Serbia after being ruled out injured.
With Darren Randolph already ruled out, Kelleher or Rochdale's on-loan Manchester City youngster Gavin Bazunu were in line for a senior debut in Belgrade on March 24.
However, Kelleher, who has been battling an abdominal tear, will miss out along with Burnley defender Kevin Long, on-loan Swansea midfielder Conor Hourihane, and Bristol City winger Callum O'Dowda.
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Blackburn defender Darragh Lenihan has been called up while West Ham midfielder Conor Coventry has been promoted from the U21 squad as replacements.
Stephen Kenny's squad have reported for duty in Manchester on Sunday where they will train on Monday before flying out to launch their Group A qualifying campaign away to Serbia.
Ireland then face Luxembourg in Dublin three days later before rounding off a busy schedule with a friendly against Qatar on Tuesday.
With reigning European champions Portugal favourites to win the group, Ireland may have their work cut out, especially as they are still yet to taste victory under Kenny.
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However, Preston midfielder Alan Browne remains defiant and believes Ireland can cause an upset and reach next year's finals
"It's a tough group," Browne said. "You know, I think any group would have been, any selection of teams. It's international football, so it's always going to be a tough one.
"On paper, people will probably rule us out, if we're being realistic, given our recent results. We haven't been doing well enough, so I'm sure the critics will have already ruled us out.
"But us as a team and a nation, we're always ones to thrive off this and be the underdog and come out on top, and that's what we're looking to do.
"We've got to be as optimistic as possible. We're going into every game to win it, be in no doubt about that.
"That's what we've always done and we want to live up to teams that have gone before us, getting through to the big games and the big stages. We want to keep that going."