Sunderland manager Martin O'Neill has refused to name specific transfer targets but has insisted that the North-East club are in the market for new players.
The Black Cats have more recently been linked with a £12m bid for Wolverhampton Wanderers forward Steven Fletcher.
"I can't obviously mention particular players, but we're definitely in the market to try to improve the squad," O'Neill told the Sunderland Echo.
"It's pretty obvious where we're looking to try to strengthen and of course we're going to be linked with a lot of players.
"It's not right to publicise what we're doing at this minute. But we have made a number of bids for a number of players and we're still waiting to hear back."
The likes of Blackburn Rovers pair Martin Olsson and Steven N'Zonzi are also thought to be on Sunderland's radar.
