McCarthy, 26, missed Everton's win over West Brom on Saturday after suffering a recurrence of a hamstring injury.
Toffees boss Ronald Koeman said after the game that the midfielder is "one or two weeks" away from fitness.
Koeman and Republic boss Martin O'Neill became involved in a row about McCarthy's fitness in November and the player missed the 1-0 win in Austria.
McCarthy's hamstring issues have restricted him to only seven Premier League starts this term and Koeman is keen to get to the bottom of it.
"He played 30-35 minutes last week and then we need to put him in the recovery group after the game," said the Everton boss.
"It's not a big hamstring injury. He will be out for one or two weeks.
"It's another step back for the boy and that's really disappointing. We need to find a solution."
O'Neill will announce the Republic's squad for the Wales game on Monday and the expectation is that the Everton midfielder will be an inclusion.
Asked if he expected O'Neill to select McCarthy, Koeman replied: "I don't know. We know it will be another nine, 10 days [before the game] and the Fifa rule is that they have the possibility to call the player.
"If they call the player the player will go and they will see how his fitness is at that time."
The Republic lead Group D on 10 points after four rounds of fixtures, which leaves them two points ahead of Serbia with Wales a further two points off the pace in third.
Everton's James McCarthy is a doubt for the Republic of Ireland's World Cup qualifier against Wales on 24 March.