Andre Villas-Boas has admitted that he is looking to add two players to his Chelsea squad this month.
Bolton Wanderers centre-back Gary Cahill is believed to be close to sealing a move to Stamford Bridge.
The identity of the second player is unknown, although Porto striker Hulk and Juventus winger Milos Krasic have recently been linked with transfers to Stamford Bridge.
"Apart from the central defender we might get one more player in, but we're not sure yet," he told a press conference.
"It's always difficult [in January]. First of all, the top talent is normally cup-tied in the Champions League, or in the different domestic competitions.
"It's difficult for the selling club to make players available. So it's normal to struggle in the transfer market."
The Blues are currently fourth in the Premier League table.
