McCarthy is yet to feature for Everton at all this season, with the midfielder not yet fit enough to play.
And Koeman admits that McCarthy will not be available for Everton’s next match, which comes against Bournemouth tomorrow.
“He’s struggling with his fitness,” the Dutch manager said. “I expect James back in training next week.”
McCarthy struggled with injury last term too, when he was left on the treatment table for large chunks of the campaign.
It seemed that the Republic of Ireland international may have moved on in the summer, but he has stayed to fight for his place at Goodison Park.
Whether McCarthy will feature much, even when he is fully fit, remains to be seen - as Everton have a wealth of midfield options.
The Toffees are under pressure to beat Bournemouth on Saturday, after making a slow start to the campaign.
Everton are currently in 18th place in the Premier League table - having won just once in their first five fixtures.