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.
Millwall have signed midfielder Guy Moussi on loan from Nottingham Forest.
The 28-year-old Frenchman has agreed a switch to The Den until January 2 having found first-team opportunities limited with Forest this season.
Manager Steve Lomas moved for Moussi after Shaun Derry left to become manager at Notts County.
Lions assistant boss Mick Harford told the club website: "Shaun left us last week and we wanted some competition in midfield.
"Guy is big, strong and athletic, and that's exactly the type of player we've been looking for."