The 26-year-old has not reached his potential since coming to Stamford Bridge in a £14 million ($18m) deal from Augsburg.
His initial struggles were made worse by a cruciate ligament injury at the African Cup of Nations with Ghana that have left him struggling to hit peak fitness ever since.
The full-back, whose deal expires in June 2022, is understood to be fully fit now and he has been training at Cobham with the loan group of players. They have played friendlies against Wimbledon and Crystal Palace Under-23s in recent weeks in an attempt to keep fit.
Rahman's move is just one of many that will be completed after the Premier League transfer window shut, with Chelsea still needing to offload a host of first-team and former loanee players.
Unfortunately, after loan deals collapsed for the likes of Marcos Alonso, Emerson Palmieri, Antonio Rudiger and Fikayo Tomori, they all look set to stay in an overloaded first-team squad.
Still, a lot are soon due to move on with Malang Sarr close to completing a season-long loan move to Porto. Similarly, Marco van Ginkel is near to re-joining PSV Eindhoven after almost two years on the sidelines with injury, while Juan Familia-Castillo is rumoured to be close to joining AZ.
Jake Clarke-Salter turned down overseas loan interest from Club Brugge and Trabzonspor to prioritise a move to the Championship once again. Although a deal isn't thought to be close, it is understood that Derby County, Huddersfield Town, Birmingham City and Sheffield Wednesday have all registered an interest.
Danny Drinkwater, Victor Moses and Nathan Baxter are among former loanees also looking for moves to foreign leagues with transfer windows still open or EFL clubs.
Some players in the youth team might make late moves too like Ian Maatsen, Lewis Bate and Henry Lawrence, but it requires them to be released from a competitive youth set up that's out to win trophies again at academy level.
Ruben Loftus-Cheek became the 25th player to leave on loan on transfer deadline day to Fulham. There are expected to be well over 30 Chelsea players out on loan this season, but it will need to be trimmed within a year as FIFA look to impose limits on clubs for stockpiling talent.