Manchester City fear midfielder Rodri could be out for a month after he picked up a suspected hamstring injury against Atalanta.
The defensive midfielder has started as a central defender in City's last two games with first-choice Aymeric Laporte injured.
"Hopefully it will be 10 days if [his hamstring] is not broken," manager Pep Guardiola said.
"If it is broken it will be three weeks or one month."
City started the season with Laporte and Nicolas Otamendi as their first-choice pairing but Guardiola has played midfielders Rodri and Fernandinho at the back this week.
Otamendi and John Stones came on in the second half against the Italian side.
"I didn't speak with Rodri or the doctor just yet but looks like a hamstring," Guardiola said.
"When one guy runs and puts their hand in the hamstring position, it is a hamstring. It looks like."