Robinho, who took a full part in training at Carrington on Monday, told the Brazilian media that he was all set to return to his boyhood club after being told by City directors that he could leave.
The 25-year-old told Brazilian radio station Radio Bandeirantes: "What's important is to be happy. The directors all agree that it's better to send me out on loan. It would be exceptional to return to Santos."
Robinho then told TV Globo a deal was almost done to return to the club where he began his career and won the Campeonato Brasileiro in 2002 and 2004.
"It's all good progress. Santos are only looking at the length of contract because they want a year and City want only six months but I think it is 90% sure," Robinho said. "Santos are talking to the staff of City and I think that within three days we can define it all."
However, Mancini denied any knowledge of an imminent Robinho exit and said he was keen for the player, who scored in City's 4-2 FA Cup fourth round win at Scunthorpe on Sunday, to stay at Eastlands.
Mancini said: "Hopefully in the end Robinho will stay here. In the next day the situation can change but at the moment he stays here and I am very happy for him.
"I think one player can stay in a squad only if he is happy - if he wants to play every game and if he wants to work every day. That is most important because the players and manager must be happy."
However, rumours persist that a delegation from Santos have jetted into England to discuss terms and Santos president Luis Alvaro Ribeiro claims a deal is in place that would allow City first refusal on talented youngsters Paulo Henrique Ganso and Neymar.
He said: "They [Manchester City] want the first choice to buy the two boys. That does not bother us because we sell the players for the best offer. If City have the conditions to match the offer, they can have the players.''
Robinho joined Manchester City from Real Madrid for £32.5 million in September 2008 but has failed to impress in the Premier League. The 26-year-old was brought on as a substitute and then subbed himself against Everton earlier in January.