Stoke could complete the signing of Bruno Martins Indi on Friday but it will not be done in time for him to play in the opening game of the season at Everton.
Potters boss Mark Hughes has been trying to get the 25-year-old centre-half back to the bet365 Stadium on a permanent basis following his successful loan spell last season.
Negotiations with Porto have proved frustrating but Press Association Sport understands a deal just in excess of £7million has now been agreed and the player has settled his own outstanding contractual issues with the Portuguese club, which had been a contributory factor in delaying the deal.
Martins Indi is due in Stoke on Friday but has yet to undergo a medical and he would need to be registered before midday to be involved in Stoke's Premier League opener at Goodison Park.
"My understanding is it's very close," said Hughes. "All being well, he should be with us today at some point and hopefully we will get that done.
"It's one that's frustrated a lot of people, not least myself, but now it's likely to get done unless there's any last-minute hitches, but we don't anticipate any.
"It's probably going to be a day too late (for Everton game). He will have a medical and that takes time, so the thinking is he will be ready to go from Monday."
Hughes confirmed that Joe Allen's former club Swansea had made a tentative enquiry about the midfielder.
The 27-year-old left the Liberty Stadium for Liverpool in 2012 before joining Stoke in a £13million deal last summer. Swans boss Paul Clement had Allen in mind as a potential replacement for Gylfi Sigurdsson, who looks set to join Everton. Clement said this week that talks regarding that deal were at a " critical stage."
"They made an enquiry," said Hughes. "It wasn't a bid or a request to buy him or anything like that. They just asked would we be willing to allow him to leave and we said no.
"I think we have to respect that they came and they did that and because of the answer they got you'd like to think they will respect our position."
Should the Sigurdsson deal go through it would take Everton's spending this summer comfortably through the £100million barrier and Hughes is under no illusions that it will be a difficult early test for his team.
"They've brought good players in but lost key players too, like (Romelu) Lukaku. Clearly Wayne Rooney has the ability to fill that space," said Hughes, who had a brief spell at Goodison Park towards the end of his playing career.
"They've got a good side and they've spent money from letting good players go, perhaps similar to Southampton a couple of years ago.
"It's always a close game when we play Everton - a draw and they won by a single goal last season. There is always a turnover of players at this stage and you don't know until you start playing where you are. We are looking forward to getting started."