The Portugal captain and World Player of the Year has been hampered by a left knee problem in recent months and was clearly below his best at the World Cup in Brazil, where the Portuguese failed to progress beyond the group stage.
"He (Ronaldo) did two sessions today and he is working well on his own," Ancelotti said at a news conference on Tuesday after Real were beaten 1-0 by AS Roma in a friendly at the International Champions Cup in Dallas.
"Let's see if in the next few days he can train with the team and can play against Manchester," added the Italian. "We have to be careful, right now we have to be calm."
Ancelotti will be hoping Ronaldo regains full fitness in time for the European champions' first competitive fixture of the 2014-15 season, the European Super Cup against La Liga rivals and Europa League winners Sevilla in Cardiff on Aug. 12.
Real have strengthened their squad with the purchase of Colombia playmaker James Rodriguez and Germany midfielder Toni Kroos and Ancelotti said there might be more movement before the transfer window closes at the end of August.
Media reports in Spain have said Real are looking to sign Costa Rica goalkeeper Keylor Navas from Levante.
"We have to think about the players who are at Real Madrid at the moment," Ancelotti said when asked about the transfer market.
"The market ends on Aug. 31 and a lot of things could happen but we have to focus on those (players) that we have."