The 19-year-old defender has signed for the Championship club, who are battling for promotion at the moment.
Harwood-Bellis is sixth choice at centre-back in the City squad, which means they have plenty of other options in that area of the pitch for the second half of the season.
Guardiola told reporters of the youngster: "He'll play in a good competition at a good historical team, he'll play real opponents.
"The academy is good for a short time but he needs to grow as a player and he doesn't have many minutes here in the first team.
"He has had two seasons training with us, there are other young lads training in their first season.
"This is the best way to see him, in a good competition."