No, he didn't. That's what Paul Joyce tweeted, but it isn't what Koeman actually said. This is what I mean about the headlines. What he actually said, word for word was: "He started at the weekend, that is no reason to have doubts about his future with Everton".
Note the use of 'that'. Not "there is no reason to have doubts about his future with Everton", not "hopefully his future will be with Everton" and certainly not "James McCarthy's future lies with Everton", just a comment that playing in our most recent game is not a very good reason for assuming somebody is on their way out.
I'm not saying he will be leaving, just that the quotes were nowhere near as emphatic as you're making out.
I am not certain that RK will want to sell James McCarthy.
He knows that playing wing back is a position alien to the player and yet he trusted him to play there.
Last Saturday it was the system that was not working rather than the player being poor and although McCarthy was disappointed to be taken off I don't think it was a reflection of the managers opinion of the player.
Atotally different question however is if McCarthy is happy to be a member of the squad and although will probably play most weeks is not a core player playing in his preferred position...he may want to take the opportunity to go to a team where he is the main man again.
I think some Evertonians are not grasping the squad concept. It is alright to say to get rid of Gibson, McCarthy, Cleverlry, Oviedo and others , but how do you put a group of twenty or more outfield players together who absolutely insist they play every week. It is easier if you have CL football, but we don't have that option...yet.