Flynn Downes is set to join West Ham United with Swansea City poised to sign Wales midfielder Joe Allen.
The midfielder, 23, had seemed set for Crystal Palace, but wanted to join West Ham after they matched the Eagles' offer.
As Downes departs, Allen is close to completing his return to Swansea.
The Swans academy product, 32, is expected to join Russell Martin's side on a two-year deal after turning down a new contract at Stoke City.
Downes, a West Ham fan, will sign a long-term contract at the London Stadium.
The Essex-born midfielder excelled at Swansea last season after joining from Ipswich Town for about £1.