A rare thing happened at Old Trafford on Saturday: Radamel Falcao won the game for Manchester United. It was an isolated moment of class in a game of unremitting drudgery. In fact, it was just about the only moment of class.

Ander Herrera played a ball into the box from the United right midway through the second half and Falcao took it down with the sweetest of touches.

In the same movement, the Colombian spun away from Sunderland’s John O’Shea and was pulled back as he shaped to shoot.

Radamel Falcao goes down under the challenge of John O'Shea and Wes Brown to win a penalty

Falcao's touch which led to the penalty was a reminder of his quality, and changed the course of the game

Brown was sent off for his part in bringing down the Colombian, but it should have been O'Shea

Wayne Rooney stepped up to convert the penalty, putting United into the lead at Old Trafford

Referee Roger East sent off Wes Brown by mistake, Wayne Rooney scored the resultant penalty and the game was effectively over.

It was a tantalising glimpse of the player Falcao used to be, Atletico Madrid’s feared penalty-box predator who could terrorise the best defences.

A few seconds later, he was substituted for Marouane Fellaini. A thunderclap of boos rolled around the stadium in protest.

In many ways, it was hard to argue with manager Louis van Gaal’s decision. Falcao was lucky he had lasted that long.

His £60 million team-mate, Angel di Maria, had been taken off at half-time after an anonymous first half.

Before the crucial penalty Falcao had been ineffectual, failing to find the form that brought him to Old Trafford

Falcao has not done enough to convince Louis van Gaal he should be signed permanently this summer

Angel di Maria was also off the pace in United's 2-0 win over Sunderland and was replaced at half time

Van Gaal insisted that Di Maria still needs time to adapt, but he should apply the same principle to Falcao

There were no complaints about that and the truth is that Falcao, 29, had been very much Di Maria’s equal in mediocrity.

Most of the time, his second touch was a tackle. It’s an old saying but it rang true for Falcao in the opening 45 minutes. The ball kept bouncing off him.

‘I was very pleased with his action for the penalty because he won it for us,’ said Van Gaal.

‘But I had to win the game and I saw at that moment that we needed to keep the ball more and with Fellaini it is more easy to keep the ball.’

Once again on Saturday, Falcao’s former knack of poaching goals from nowhere appeared, once again, to have deserted him.

Sure, the service he received was hardly up to the standard that United forwards of the past have been used to.

Falcao looks on disappointed as another United chance goes begging, while Rooney bends over

The Colombian striker has become more notable for missing chances than scoring them since joining United

Falcao's goals have been few and far between, but his match-winning touch showed he has still got it

But on the few occasions that Ashley Young, United’s liveliest forward, did force his way to the byline and cut back crosses, Falcao was out of the picture. In that first half, he was marked out of the game by former United defender Brown, who didn’t give him a kick. Brown is a good player but he’s not exactly Thiago Silva.

In the circumstances, Falcao was lucky to make it back out for the second half. He has scored just four goals in 17 league appearances for Manchester United this season. His threat has been negligible.

The consensus is that time is running out for him to persuade Van Gaal and the rest of the United hierarchy that it would be responsible for them to spend the £40m to make his loan deal from Monaco permanent at the end of the season.

Falcao, once so dynamic a poacher in the penalty area, was rarely in the right place at the right time

The striker continued to work hard throughout, but until the penalty showed very little quality

The 29-year-old applauds the Manchester United fans, who have stuck by him through his form troubles

However wonderful a striker Falcao used to be, the hard truth is that on the basis of what United have seen so far, if they had to make their decision today, he is simply not worth it.

And yet having invested so much in him emotionally, having hailed him as a goalscoring hero when he arrived in the summer, United’s supporters are reluctant to give up on him just yet.

To their credit, they have been relentlessly supportive of Falcao. Their yearning for him to rediscover his quality has never curdled into disillusionment.

And to Falcao’s credit, he has never stopped working. That is part of the reason United fans have stuck by him.

If Di Maria has developed a tendency to drift aimlessly through games, Falcao has never stopped running himself into the ground.

Falcao shakes hands with United staff members after being replaced on the hour-mark on Saturday

Marouane Fellaini was brought on by Van Gaal to help United retain possession better once in the lead

And while he is still capable of producing a moment of magic like Saturday's pivotal moment, there will still be those who will dream he can return to his former self. In those circumstances, might Van Gaal have kept Falcao on the pitch for a while to see if he could capitalise on the confidence that winning that penalty had brought him?

If there is even a slim chance of bringing a player of his pedigree back to life, then surely it is worth taking.

Van Gaal had said on Friday that the reason United are not challenging for the title is that they do not have a 20-goal-a-season striker.

But Falcao was brought to the club to be that striker. Resurrect him and United’s chances of making the top four and securing a place in the Champions League next season will improve dramatically.

Falcao celebrates with Rooney, and could yet prove to be important in Manchester United's push for Europe

If Van Gaal can help his forward to find confidence, he could have the striker he thought he had signed

Instead, the chance to breathe confidence back into him was missed and when the final whistle blew, Falcao walked alone along the touchline, applauded all the way by the home supporters.

Many saw Van Gaal’s decision to substitute him as a sign that he has already made up his mind to let him go.

But when the United boss spoke about Di Maria afterwards, he was at pains to point out that it takes time to settle in the Premier League.

The same logic applies to Falcao, maybe even more so given that he is still recovering from a serious knee injury that ruled him out of last summer’s World Cup.

While he can still turn a game with one moment of brilliance, it would seem like folly to abandon him now.