Andy Carroll has not travelled with Liverpool for Thursday's Europa League qualifier against FC Gomel in Belarus.
The England striker was withdrawn from the squad with a slight groin strain on Wednesday morning but his future remains increasingly unclear, reports the BBC.
West Ham are still trying to persuade Carroll to join them after having a £2m loan offer accepted by Liverpool.
Newcastle retain a strong interest in their former player but have adopted a watching brief on the situation.
UEFA rules allow a player to represent one club in the Europa League qualifying round and another in the group stages.
That means that, if Carroll plays for Liverpool during qualifying, he could potentially play for Newcastle, who have secured a place in the group stages.
New Liverpool manager, Brendan Rodgers is also without Luis Suarez and Craig Bellamy, both of whom are on Olympic duty, while new signing Fabio Borini, like Carroll, has recently returned from an extended holiday after Euro 2012.
Although West Ham's loan offer was accepted, Carroll has indicated he does not want to join the Hammers, on loan or on a permanent deal.
Newcastle remain confident that if Carroll leaves Anfield he is interested only in returning to Tyneside.
Liverpool, who signed Carroll for a club record £35m in January 2011, have already turned down Newcastle United's bid to re-sign the player.
Meanwhile, the deadline for Demba Ba to activate a £7m escape clause in his Newcastle contract passed without a bid Tuesday.
Despite interest from Galatasaray and Rubin Kazan, Ba looks certain to begin the season on Tyneside.