Former Brighton and Chelsea boss Graham Potter is understood to be close to agreeing a deal to take over as the new boss at the London Stadium.
Lopetegui took training as usual on Tuesday but his spell in charge looks likely to come to an end less than eight months after he was appointed to replace David Moyes.
The Hammers on Wednesday morning called off the press conference at which the present boss was set to preview Friday's FA Cup third-round tie at Aston Villa.
Former Spain national coach Lopetegui, 58, appears set to pay the price for back-to-back heavy defeats by Liverpool and Manchester City over the Christmas period, with the Hammers a lowly 14th in the Premier League.
They have picked up just eight points from their past eight matches.
Potter, 49, has been out of management since he was sacked by Chelsea in April 2023, just seven months into a five-year contract.
He began his managerial career at Swedish club Ostersund and successful spells with Swansea and Brighton prompted Chelsea to appoint him to replace Thomas Tuchel in September 2022.
But Potter won just 12 of his 31 matches in charge.
