Left back is an area Keane had been looking to strengthen and McCartney, who left Sunderland for the Hammers two years ago, was earmarked as the man for the role.
"We're hoping to bring one more player in but if it doesn't happen, there's no panic," Keane told the club's official website.
Several fringe players have been tipped to leave the Stadium of Light as well and Keane admits a couple could move on, either on loan or in permanent deals.
The Sunderland boss added: "I've got two or three more players who I wouldn't stand in their way if an offer came in for them."




