Santos will pay all of Robinho’s contract terms, including wages and bonuses.
Robinho joined Manchester City in a British-record £32.5million deal from Real Madrid and impressed in his first season at Eastlands.
The 26-year-old has struggled to make an impact this season and is keen on regular first-team action.
Mancini told City’s official website: “Robinho is someone who needs to be playing regularly and we wish him well for the period of his loan.”