James Vaughan has completed his permanent move to League One leaders Wigan Athletic.
Sunderland have already lost top scorer Lewis Grabban this month after the striker made it clear his future wasn't on Wearside with interest in the AFC Bournemouth striker from other Championship clubs.
And Vaughan has now left Wearside for Wigan for an undisclosed fee, believed to be in the region of £300,000.
Sunderland signed the striker for £500,000 from Bury in the summer but he has struggled on Wearside, scoring just twice this season.
Vaughan says it was an “easy decision” to leave Sunderland for League One leaders Wigan Athletic.
"This is a great club and the manager was very keen to get me here," said Vaughan.
"When a manager tells you that you are his only target, and how much he wants to get the deal done, it’s an easy decision."
Vaughan has signed an 18-month deal.
Coleman is targeting two strikers this month and remains hopeful of landing his targets soon, though he was coy on links with Burnley striker Jon Walters.
On the Vaughan deal, Coleman added: "It is a cash deal and I don't think it has worked out here.
"We are bottom of the league, we have been here six months with this team.
"What is the point in keeping things the same, we have to change things. Simple as. It is an area we have to change.
"Whether we kept him or not I still wanted two more in.
"Without him, two don't change, we also have young Josh Maja who will get better. We still need two in there."
Elsewhere, Sunderland have cancelled the contract of goalkeeper Mika, who failed to play a first-team game for the club.