Ronaldo was pictured jogging round United's Carrington training base on Friday morning after being given the green light to step up his recovery from ankle surgery.
But Ferguson remains cautious. He would prefer the 23-year-old to come back and stay back rather than return a week or two earlier and risk a further spell on the sidelines.
"If a player is out for a certain period there is no point rushing it," said the Red Devils boss. "You may as well wait the extra week or two to make sure they don't suffer any setbacks.
"Sometimes the age of a player helps with their recovery. Cristiano may get back quicker. But we are not putting him under any pressure.
"We have to let the physios do their job properly."
But Ferguson is certainly delighted with the work Ronaldo has done so far.
"The plan was to give him one month of rehabilitation work, jogging and aerobic work in the gymnasium," he said. "It is difficult to say with young players and long-term injury but Cristiano is making good progress."