The Telegraph claimed yesterday that the clubs are £5m apart on the fee but neither will budge even though a verbal agreement of £45m, paid in full without add-ons, had been reached earlier.
Koeman and the Blues were hopeful of having him in place by the time the new season kicked off but that now looks to be a remote possibility unless a deal can be hammered out within the next few hours.
The Telegraph's suggestion is that the negotiations are on the brink of collapse but Koeman played down those fears at his pre-match press conference this afternoon.
"It's still close," the manager said. "That has not changed. I heard some rumours that the talks broke down but we are still in negotiations with Swansea. I have heard the comments of Paul Clement, the manager of Swansea.
"Of course everyone would like news, that it is better for us and it is better for them. Everybody knows the window is difficult and it is always a game between the selling club and the buying club.
"But we are close. Let's hope we get an agreement as soon as possible."