The 19-year-old right-back played 13 games for the Second Division club last season.
He has made three appearances for Manchester City this season - one in the League Cup and two in the Champions League.
Maffeo, who has represented Spain at U19 level, joined City in 2013 and has come through the club's academy system.
Manchester City defender Pablo Maffeo has joined Spanish side Girona on loan until the end of the season.