The Portugal international moved to the Santiago Bernabeu in 2009 following a trophy-laden spell under Alex Ferguson at United.
Since his arrival in Spain, Ronaldo has gone on to establish himself as arguably one of the greatest players of all time, maintaining an outstanding goalscoring record at the Santiago Bernabeu.
His record 17 goals in last season's UEFA Champions League helped the club to a 10th European Cup triumph, but there have been recent whisperings that the 29-year-old yearns for a switch back to Old Trafford, with former Real president Ramon Calderon claiming the forward has become disillusioned with some of the high-profile departures from the Spanish capital.
However, in a press conference on Friday, Van Gaal moved to dampen any such talk of a move for Ronaldo.
"When it is possible, what I said with [Radamel] Falcao, players like Ronaldo give a lot extra to selection or to a team," he said.
"But I don't think Real Madrid shall sell him.
"It's always a discussion in the papers and I don't think the media shall buy Ronaldo."
Following the arrivals of Angel di Maria and Falcao during the transfer window, Van Gaal has an embarrassment of riches going forward, and the Dutchman conceded the make-up of his squad may see him move away from the 3-5-2 formation he had favoured previously.
"I started with another system," he said. "Now we have bought players in and you have to look at their qualities
"I don't think any player is fixed. Only the captain [Wayne Rooney] has more privileges.
"Falcao is a very good striker and I like [Robin] Van Persie. Then we have Rooney, [Adnan] Januzaj and [James] Wilson. We have five players for two positions.
"Januzaj has to compete with very strong strikers. When we play 4-3-3 he should have more chances to play."
