Chelsea, who usually ask their players to sign new deals before heading out on loan, decided to make an exception for Cahill. Although he's currently club captain, the 32-year-old has played just 21 minutes of Premier League football this season.
Blues boss Maurizio Sarri made it clear early on Cahill would get little playing time. It's believed Cahill doesn't have the technical skills to play the kind of high-tempo, possession-based football Sarri craves.
Cahill admitted in September he'd likely have to find a new club in January to revive his career.
"I don't want to jump the gun, but as things stand at this time, probably, yes," Cahill told reporters, according to Reuters' Simon Jennings. "I'm not a guy who is willing to accept not playing. It's all about playing.
"You career's short enough as it is. I've got maximum respect for everybody here at the football club, for the fans and all the players. But sometimes you have to make tough decisions to keep your career going forward."
The defender won the Champions League trophy in 2011-12, his first season with Chelsea, before claiming the Premier League twice.