Gill said: "We saw them (the owners) at the Champions League final and the speculation was already present then. It was a short, quick conversation.
"Under the PLC regime, we would not have had to sell him but we would have had to be more public.
"As it is we have had one phone call, one chat in Moscow and the decision was made. Full stop."
Ronaldo is only one year into a five-year deal and has repeatedly refused to commit himself to the club.
United, however, are relaxed about the situation after manager Sir Alex Ferguson met the player in Portugal.
Gill said: "You cannot say what will definitely happen in a year's time. But by then he will still have three years left on his contract.
"Let's not worry too much about it. He is at the best club and Alex is very comfortable about it.
"We may give him another contract next summer, you never know. I have not, however, had detailed discussions with his advisors."