The Merseyside club announced on Monday they had agreed an £8.6million fee with Twente for Fer but the deal has hit a snag after the 23-year-old travelled to England for a medical.
Medical staff at Goodison Park reportedly raised concerns regarding the player and Everton have gone back to Twente in an attempt to renegotiate the deal.
It is thought the Toffees want to pay a smaller amount up front with the remainder dependent on appearances and other factors, but the Dutch club are reluctant to accept the proposed changes.
If the Dutchman does arrive at Goodison, Moyes insists it will not be to replace Everton's influential Belgian midfielder Fellaini.
"I read something about him replacing Fellaini and that's the biggest load of tosh I have heard," he told the Daily Mirror.
"That's nonsense, whoever wrote or said that.
"They are different types of players. No, that's not the reason for bringing him, that's for sure."
Moyes feels the addition of Fer would help lift his Everton squad as they battle for a fourth-place finish in the Premier League this season.
"I felt that we are in a really strong position and that we should try and strengthen that position and stay there if we can," he said.
"I would hate to look back and think I hadn't given that a go or made any attempt to do that.
"The squad needs help. I think the squad has done brilliant to get where it has got, but it could do with one or two additions."
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