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.
Wigan have signed goalkeeper Joel Robles on loan from Atletico Madrid until the end of the season.
The Spanish club, second in the Primera Division and ahead of city rivals Real Madrid, had allowed Robles to spend a trial period at the DW Stadium, and boss Roberto Martinez was sufficiently impressed to bring the 22-year-old into his first-team squad.
Atletico confirmed the deal tonight in a statement on their website, which read: "Atletico Madrid and Wigan Athletic have reached an agreement so that Joel Robles, after a trial period with the English club, will play on loan until June 30 with the Premier League team.
"The goalkeeper will return to the 'rojiblanco' at the end of this loan period."
Robles has yet to break into the Atletico first team on a regular basis, with Chelsea goalkeeper Thibaut Courtois currently on loan with the club and the established preferred choice of coach Diego Simeone.
The 6ft 5in shot-stopper had a loan spell with Rayo Vallecano last season before returning to the Vicente Calderon stadium.
At Wigan he will provide competition for number one Ali Al Habsi and reserve Mike Pollitt.