Sunderland boss David Moyes has confirmed that striker Fabio Borini is facing up to three months on the sidelines with a groin injury.
The 25-year-old Italian tore an adductor muscle while taking a free-kick during Saturday's 1-1 Premier League draw at Southampton, his first appearance since the opening day of the campaign.
Moyes told the Sunderland Echo: "Borini, we expect to be out for three months, that is a rough guide. There is a chance it could be a bit quicker.
"We are being told it is three months though, an adductor that came off the bone."
Borini's misfortune has left Moyes with just one senior frontman, 33-year-old Jermain Defoe, and youngsters Duncan Watmore and Joel Asoro, who is just 17, to provide the back-up after his search for reinforcements ended in frustration.
Moyes, who could now look at free agents, added: "We worked incredibly hard to try to get a striker in all through the window.
"We didn't get anything late on, which we thought we would do. We may have to go and look into somebody who could give us an alternative for coming off the bench or a wee bit of back-up through the season."
Borini will join long-term absentees Vito Mannone, who has now undergone surgery on ruptured elbow ligaments and will be out of action for a similar period, and Sebastian Larsson in the treatment room, while key midfielders Lee Cattermole and Jan Kirchhoff have not managed a single appearance between them so far this season.
Borini spent the 2013-14 season on loan at the Stadium of Light from Liverpool and helped the Black Cats reach the Capital One Cup final, where they were eventually beaten 3-1 by Manchester City after he had given them a first-half lead.
The striker returned to Anfield determined to force his way into the starting XI, but left for good in August 2015 when he finally accepted Sunderland's overtures and completed a move to Wearside for an initial £8million.
Meanwhile, Mannone's deputy Jordan Pickford has returned from international duty with England's Under-21s with a slight thigh strain, although he is expected to be fit for the home clash with Everton on September 12.
Sunderland also tried to sign another keeper as Wednesday night's deadline approached with Norwich's John Ruddy and Crystal Palace's Wayne Hennessey understood to be among their targets, although it was Boavista's Mika Domingues who came closest to arriving, only for time to run out.
Moyes said: "We want to try to give Jordan the chance to show what he can do - he is another young player here - but we will definitely have to get a cover of some sort, or somebody who can challenge Jordan."