Town centre-half Elkan Baggott has been recalled from his loan spell with League Two Gillingham in order to join League One Cheltenham on the same basis for the second half of the season.
The Indonesia international moved to the Priestfield Stadium in the summer and made 27 starts and two sub appearances for the Gills, scoring three goals.
"I'm delighted to be here,” the 20-year-old told the Robins official website. "I'm ready to get going, and help in the best way I can to assure we stay in this league.
"I want to help out at both ends of the pitch. Obviously I need to do my defensive work, but I want to chip in and help add goals too.”
In June, Baggott, 20, signed a new deal with the Blues which runs until the summer of 2025 with the club having an option for a further season.
Elsewhere, former Blues striker Joe Garner, 34, has joined Carlisle United from Fleetwood on an 18-month contract.