Roberts joined City from Fulham in 2015, but has only made three first-team appearances for the Citizens.
The attacker has spent the last two-and-a-half seasons on loan at Celtic - scoring 18 times in 78 appearances for the Scottish giants in all competitions before returning to the Etihad Stadium.
Roberts was widely expected to join Huddersfield Town on loan last week, but the move fell through at the final moment.
According to the Daily Mail, the 21-year-old is now on the verge of completing a loan move to City's sister club Girona, having arrived in Spain on Tuesday to sign the deal.
City are believed to have paid Fulham £12m to sign Roberts on a long-term contract in 2015.