The Black Cats made a breakthrough in the transfer window, when they snapped up Jake Clarke-Salter from Chelsea on loan.
Sunderland realise that their work cannot stop with the addition of the centre-back though, and Coleman has confirmed that other deals are being worked on.
“It’s not easy to get the right person because of course there are other clubs in a similar predicament - a similar situation - to us,” Coleman admitted.
“To get loan players it is a bit of a dog fight, but I think Jake is a good start for us and there’s still maybe two, three or four more that we’d like to do.”
Clarke-Salter should bolster Sunderland’s defensive options, and could come straight into Coleman’s line-up.
The Black Cats have their eyes on strengthening all areas of their squad, after what has been a disastrous first half of the campaign.
Sunderland are currently sit at the bottom of the Championship table, and they are firmly locked in a relegation battle.
Coleman’s side have been linked with a whole host of players, but they have only a limited budget to work with.
Sunderland will have to sell before they can buy this month, meaning a number of fringe players have been put on the market.
Sunderland are next in action this weekend, when they take on Cardiff City.