As he came off, Ronaldo uttered some words and threw his coat to the ground before sitting on a step in the dugout.

Rangnick said Ronaldo's reaction to being taken off was "normal".

The German also told BBC Sport: "He was not happy but he came back from injury. I was happy to have him on board for today's game, especially after Edinson Cavani could not train."

Rangnick indicated that his decision to substitute Ronaldo was driven in part by the experience of losing a two-goal lead late on at Aston Villa last Saturday, in a match the Portugal captain missed through injury.

United drew 2-2 at Villa Park, having been 2-0 up with 13 minutes to go, and Rangnick was keen to avoid a similar late stumble in west London.

Rangnick said: "I told him [Ronaldo] we were 2-0 up and we have to learn lessons from Villa Park. After that game, I was angry with myself for not changing to a back five.

"Today was exactly the same situation and I did not want to make the same mistake again. I said: 'Listen Cristiano, you are 36 and in great shape, but when you are a head coach, you will see it through the glasses of a head coach.'

"My job is to take the decisions in the best interest of the team and the club and I hope he sees it the same way."

'Ronaldo provided unnecessary sideshow' - analysis

Chief football writer Phil McNulty

Manchester United were well in control when Rangnick decided to remove Ronaldo with 20 minutes left and send on Marcus Rashford.

It was hardly controversial - indeed it was perfectly logical in the circumstances - but we were treated to the full range of Ronaldo amateur dramatics as he walked off at snail's pace, shaking his head and muttering before having a rather comical struggle with his coat in the dugout.

All in all, this was not a happy Ronaldo. His ego provided a completely unnecessary sideshow to United's win, which was pretty much sealed by the time he was taken off.

Rangnick was spectacularly unmoved as Ronaldo fumed but was then completely justified in his decision as Rashford finished Brentford off.

United's interim manager leaned over to give the pouting Portuguese what was presumably an explanation for his decision. Not that he needed to. Rashford's goal was explanation enough.

It was a needless exhibition by Ronaldo who, for all his brilliance, still gives off the air of a player and personality who almost thinks he is bigger than Manchester United.

Ronaldo does himself no good with such antics - especially when the manager's change worked so successfully.

It is not the first time this season that Ronaldo's ego has appeared to override team considerations. Rangnick's explanation that he was conserving the 36-year-old for the games ahead was far more acceptable than his superstar's behaviour.

Ronaldo may still be able to produce those flashes of genius, as he did in the build-up to United's second goal, but for all his fitness, he is not the athlete he was and occasionally needs protecting from his desire to play every minute of every game.

It is also a poor look when he shows such flagrant disrespect for a manager's perfectly reasonable decision, so it never does any harm to remind Ronaldo every now and then that Manchester United are not run for his benefit. The tail does not wag the dog at Old Trafford.

Rangnick got it right. Ronaldo got it wrong.

Elanga and De Gea impress the boss

Anthony Elanga scored his first goal of the season for Manchester United

Manchester United's three goalscorers at Brentford - Anthony Elanga, Mason Greenwood and Marcus Rashford - all came through the club's academy.

But it is 19-year-old Swede Elanga who has impressed Rangnick the most, with the manager revealing he refused to send the teenager out on loan in the January transfer window.

"I must say from the very first day from my first training session, he showed up," said Rangnick. "l had heard his name before and I was in my hotel room watching videos of him on YouTube, I thought this boy was really good.

"He was almost on his way out on loan. I told him: 'You will not go out on loan, you will stay here.' He has developed in training."

United were fortunate to go in goalless at half-time as Brentford missed numerous chances, having eight shots and seeing three saved by the in-form David de Gea.

The Spanish goalkeeper was furious when he failed to keep a clean sheet as Ivan Toney poked in a late consolation for the home side.

Rangnick told BT Sport: "He has been doing that the last couple of weeks - brilliant saves in first half. He is one of the best keepers in the world, I would say."