Aguero missed City's 3-0 win over Watford in the FA Cup third round today after suffering the problem late in the 3-0 win over Stoke on New Year's Day.
"The studies confirmed I have a torn muscle," Aguero wrote on his Twitter account tonight. "We have to keep on thinking positive and try to recover in the best way possible.
"For that, I've travelled to Italy where a specialist is treating me. I'll keep you up to date in how the injury evolves."