The midfielder has been linked with a move away from the DW Stadium all summer, and it is believed that the Toffees have already had a bid turned down by the Latics.
While he admits that McCarthy could leave on Monday, Whelan insists that Roberto Martinez must fork out more for the player.
"If Everton lose [Marouane] Fellaini and [Leighton] Baines, they are going to get their £38m or whatever," Whelan told The Sun. "They've already made one offer for McCarthy, which wasn't good enough. Roberto knows what he's valued at.
"You've got to be talking £14m or more. Are they a long way off? Probably £2m, but we're sticking because we've got to replace him. That sounds a lot of money but when you look around at the moment, all the extra money in the Premier League, it's just going mad.
"If we go and look for somebody, it's starting at £5m-£6m. We're sat there and if Everton sell their midfield lad, Fellaini, they're going to come for ours. We want to replace - but can we?"
The transfer window closes at 11pm on Monday.