City acquired a 44.3% stake in Girona 12 months and sent Pablo Maffeo and Douglas Luiz on loan there last season in a bid to expose them to more regular first team football.
For 21-year-old Roberts, who joined City from Fulham for around £12m, it represents another chance to impress away from the Etihad Stadium after spending the last two-and-a-half seasons at Celtic in the Scottish Premiership.
After a promising 2016/17 campaign, injury cruelly hampered the player last season and he was limited to just 15 appearances in all competitions as a result.
Girona will begin their La Liga season on Friday night against Real Valladolid, following that up with a huge clash against Real Madrid the following week. The team is also due to visit regional rivals Barcelona at Camp Nou before the end of September.