Mick McCarthy fears the cross-channel play-offs could affect the build-up to Ireland's Euro 2020 qualifiers in June.
Potentially 11 players could feature in play-offs, although McCarthy does expect David McGoldrick, Enda Stevens and John Egan at Sheffield United to gain automatic Premier League promotion with the Blades.
He also has two at Aston Villa (Glenn Whelan and Conor Hourihane) and one apiece at Portsmouth (Ronan Curtis), Bristol City (Callum O'Dowda), Charlton (Josh Cullen) and Derby (Richard Keogh), while Darron Randolph at Middlesbrough has a very outside chance.
That's the championship. In League One, Luton's James Collins should go up automatically, though it's not set in stone as yet.
Involvement in the play-offs would prevent players from travelling to the Algarve for a pre-qualifiers camp in late May.
"If Villa get in then I think they'll be in it to the final, they're really in form," said McCarthy.
"Sheffield United will get the points and they're playing (relegated) Ipswich on Saturday.
"The ones in the play-offs, they're on the 16th and 17th, and then 26th and 27th for First Division and Championship.
"But it is what is, I can’t do anything about it. When we get them in, most of them have played 30 or 40 games. They’re all fit, it’s a matter of just keeping them there."
McCarthy had tried to arrange a behind closed doors friendly in Portugal but it proved impossible, so his squad will play the under-21s on their return - again, behind closed doors.
But he knows he can't bring a large panel to Portugal given the time of the season.
"I’m not into bringing a load of players and saying, ‘Just come in and we’ll let you go on the 28th and go home'," McCarthy said.
"I can only play 11 when it comes around to it on the 7th and the 10th of June.
"If I was saying to some who have not been involved, ‘Would you like to come to Portugal and be involved in that camp?’ I think they’d jump at it.
"It’s a bit of a dilemma, I understand that."
O'Dowda has been out injured but McCarthy expects him to return soon.
Mick McCarthy backs rejuvenated Shane Long to make a huge difference to Ireland's Euro 2020 push
"I spoke to (Bristol manager) Lee Johnson and his injury has taken longer than anybody anticipated or had hoped for.
"But I spoke to Callum by message and he's hoping to be back on Saturday, although I didn't get that feeling from Lee.
"He said if not, then Tuesday. They have three games left. They've Derby on Saturday, which will be pretty much a (play-off) decider."
McCarthy was pleased that James McCarthy had involvement for Everton against Manchester United.
"He got 15 to 20 minutes with added time," said the Ireland boss. "It's nice to see him on the pitch and to see that he's fit enough to be involved.
"I spoke to him, it would be nice to have him involved."
McCarthy confirmed that Patrick Bamford has no chance of involvement in June as he hasn't got his passport.
The Leeds striker had previously asked not to be considered until the season was over.
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