Wigan are understood to have accepted a £13m bid from Everton for James McCarthy.
The Toffees have also completed the season-long loan signing of Chelsea striker Romelu Lukaku and a loan deal for Manchester City midfielder Gareth Barry.
Wigan chairman Dave Whelan said earlier today that Everton would need to offer at least £14m if they wanted to sign the Latics midfielder - but it appears an offer £1m short of that has in fact been enough.
Whelan said this evening: "Why they leave it so late, I do not understand. But we have accepted the offer from Everton for James McCarthy."
Whelan spoke to journalists during a promotional visit to the K Club in Kildare earlier today when he took a call from Everton boss Roberto Martinez regarding the 22-year-old Republic of Ireland international.
However, Whelan told the man who brought the FA Cup to the DW Stadium last season that he would have to come up with at least £14m.
News of the deal would suggest Everton have sanctioned the sale of Marouane Fellaini to Manchester United.
Whelan told the Irish Independent: "Roberto is chasing James. If Everton sell Fellaini, they are going to come in again for our boy.
"It depends whether Fellaini goes today. I have heard that he's definitely going.
"If Fellaini goes, Everton are going to get their £30m or whatever. Roberto knows what James is valued at, so they've got to come back in with the right amount. You've got to be talking £14m or maybe a little more."
Lukaku has also agreed a loan move to Everton, revealing the news on his Twitter feed.