Birmingham have cancelled the contract Borja Oubina by mutual consent.
Oubina had been on a season-long loan at St Andrews after arriving from Celta Vigo in the summer.
The Spanish international suffered a serious knee injury just 13 minutes into his debut against Liverpool and has not played since.
All parties have now decided to cancel the loan deal and allow Oubina to return to Celta Vigo to continue his recovery from injury.
A Birmingham statement read: "The decision to cancel the season-long loan has been made in the interests of both parties and will allow the player to return home to Spain.
"We wish Borja all the best in his future career."