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.
The 25-year-old has scored 23 league goals for Atletico since joining from Deportivo La Coruna in 2011. The Asturian played a key role as the capital club won the Europa League, UEFA Super Cup and the Copa del Rey.
He told clubatleticodemadrid.com: "I'm very happy with the renewal. To continue at Atletico was always my first target. The team is great and I want to be at the best level to help the group stay the same."
Adrian has scored four goals so far this season and Atletico are currently tied with Barcelona for top spot in La Liga.