Republic of Ireland boss Martin O'Neill says a row with Roy Keane may have prompted Harry Arter to pull out of the squad for Thursday's game with Wales.
O'Neill revealed last week that Arter and Jonathan Walters were involved in a training ground altercation with Irish assistant boss Keane in the summer.
Arter, 28, has opted out of the squad for Thursday's Nations League opener.
"That might be part of the reason, yes it could well be if that's the case," O'Neill said of Arter's row with Keane.
Following his loan move from Bournemouth, Arter played the full game for Cardiff on Sunday in a 3-2 defeat by Arsenal in the Premier League.
"He's concentrating on his club football at this moment. I think he wants to just get back on track," said O'Neill on Monday.
"His club appearances have been few and far between just recently and he wants to concentrate on that."
O'Neill says Arter could return in future
O'Neill indicated there could yet be a way back for Arter, who would have gone to the Euro 2016 finals but for a last-minute injury.
"He's a very decent footballer. Obviously, things have stalled for whatever reason at club level. He wants to get that going again and as I said, if he clears his mind and all the issues have been resolved, I don't see why not."
O'Neill has trimmed his panel down from 31 to 26 for Thursday's game in Cardiff and a friendly against Poland on 11 September.
Southampton striker Shane Long will miss the games because of a foot injury while defenders Darragh Lenihan and Greg Cunningham drop out of the squad along with goalkeeper Kieran O'Hara, who will link up with the U21s.
Preston striker Callum Robinson and Norway-based goalkeeper Sean McDermott remain after being handed first senior call-ups by O'Neill.
Northampton-born Robinson, 23, qualifies for the Republic through his maternal grandmother, who is from Monaghan.
McDermott, who plays for Kristiansund, has represented the under-21s.
Robbie Brady, Scott Hogan, Sean Maguire and James McCarthy are all also unavailable because of injury.
Republic of Ireland squad
Goalkeepers: Doyle (Hearts), McDermott (Kristiansund BK), Randolph (Middlesbrough)
Defenders: Coleman (Everton), Christie (Fulham), Doherty (Wolves), Duffy (Brighton), Keogh (Derby County), Clark (Newcastle United), Long (Burnley), Ward (Burnley), Egan (Sheffield Utd), Stevens (Sheffield United),
Midfielders: Judge (Brentford), Hendrick (Burnley), Hourihane (Aston Villa), Browne (Preston), Williams (Millwall), Meyler (Reading), Horgan (Hibernian), O'Dowda (Bristol City), McClean (Stoke City)
Forwards: Walters (Burnley), Burke (Preston), Robinson (Preston), O'Brien (Millwall)