United ace Rashford has been told he is not producing enough when he gets into the final third.
That is the opinion of club legend Parker ahead of the Manchester derby this afternoon.
The Red Devils travel across town to face their local rivals Manchester City at the Etihad.
Ole Gunnar Solskjaer has insisted he will push them all the way in the Premier League, sitting third behind them in the table after Leicester’s late win over Brighton on Saturday night.
But with 14 points separating them, their chances of catching up with City might be too far already.
Nevertheless, this could be the match that ultimately decides the Premier League champions – with City in ferocious form.
Pep Guardiola’s men are on a 21-match winning streak and United will need all the firepower they can get to stop them.
That is where Parker has felt let down by Rashford, who has scored nine in the Premier League this season after 27 matches.
For comparison, last year the England international had netted 17 times in 31 league appearances.
Anthony Martial and Mason Greenwood were also told to up their game.
He told the Mirror: “Everyone talks about Rashford and I’m pleased with what he’s done off the pitch.
“But he’s not producing regularly enough on it in terms of goals and performances.
“With Greenwood I understand people will say he’s only 20. But I’d say we’re getting to the point where we need to see more from him because he has the ability.
“You see what Ryan Giggs was doing when he was 19 and 20 and Greenwood isn’t in the same league.
“I accept you can’t compare them as players, but even when it wasn’t happening for Giggsy he was still getting on the ball and trying to be a direct threat.
“Greenwood disappears too often in games and you’re waiting for the odd shot from him. That’s not enough, he has to be more involved.
“And don’t get me started on Anthony Martial. He has talent but shockingly doesn’t look as if he wants it enough.
“That’s why the one player who has to play in every single game is Edinson Cavani.
“With the other three it’s like going to the circus and having a juggle up – you don’t know what you are going to get from Rashford, Martial and Greenwood.“