Sadlier out of World Cup
The powerful hit-man was a shock inclusion in the squad for next week's friendly with the United States, but now he has been forced to pull out.
Sadlier, who won his first cap against Russia in Februray, has been troubled with a hip injury for some time now and he has been booked in for an operation to cure the injury.
He will continue to play through the pain barrier for Millwall as they bid to make the First Division play-offs, but McGhee has agreed with McCarthy that he should travel to the Far East.
"Richard won't be joining the squad for next week's game, however, if he feels that he can play a part for us and be on the bench, so be it," said McGhee. "It is up to Richard himself to decide.
"He is booked in for an operation on his hip at the end of the month and will have it regardless.
"It is obviously a devastating blow for him to miss out on the World Cup, but we shouldn't get carried away here. He has done superbly well to get to the fringes of the Irish team, but Mick would probably have stuck with the boys who have got his side to the Finals in the first instance.
"Richard would perhaps have gone in the event of another player pulling out through injury. On the positive side, he has time on his side and will, I'm sure, be a key figure when it comes around to the European Championships."