Rashford is on-loan this season at Barcelona, where there is a permanent option worth €30m.
It's been suggested Carrick would like to see Rashford back at United should he take the job long-term.
But ahead of tonight's clash with Everton, the Geordie stated: "It's difficult to say, because circumstances at certain times that I have not been involved in.
"It's difficult for me to comment really. I think the fact he's come through the academy and had such a big impact here is a positive, and as a club, he's had some really big moments and good moments.
"And I've shared some with him in the past. So, football throws up certain things, and obviously certain players. You can't stay here forever, and things happen, that's how it is."
