Celtic boss Ronny Deila says keeping his best players will take priority over acquisitions in the transfer window.
Chelsea striker Fernando Torres is understood to be set for a return to Atletico Madrid, according to Sky sources.
Cardiff have completed the signing of defender John Brayford from Derby on a four-year contract.
The Bluebirds had already agreed a fee for the 25-year-old, believed to be around the £1.5million mark, and the formalities of the deal have been quickly wrapped up.
Brayford told Cardiff City Player: "When I heard Cardiff were interested in signing me then I was obviously very interested, especially at the prospect of playing in the Premier League and testing myself at the highest level.
"Derby will always be a special club to me, but this was an opportunity I couldn't ignore."
The former Crewe and Burton player made 117 appearances for Derby after making the move to Pride Park in 2010. He made 43 appearances under Nigel Clough in the Championship last term.