Kenny Miller admits Rangers will have to show serious improvement at Old Trafford after the striker again rescued the Light Blues in the Clydesdale Bank Premier League.
The Scotland striker netted his seventh goal of the season to secure a 2-1 victory over Hamilton at New Douglas Park on Saturday.
Miller's 90th-minute strike seal the club's third 2-1 victory in four SPL matches and followed his late winner against St Johnstone in their previous encounter.
The 30-year-old was rested following his international exploits for Scotland, where he grabbed another crucial goal against Liechtenstein.
But he was needed off the bench as Rangers struggled to regain the ascendancy after Madjid Bougherra put through his own net to cancel out an early opener from Nikica Jelavic, who is ineligible for tomorrow night's Champions League clash against Manchester United.
And Miller knows they cannot afford to play below their best when they face Sir Alex Ferguson's side.
"We'll be playing one of the best teams in the world, so we're going to really have to up it," Miller told BBC Scotland.
"If you ask the manager or any of our coaches, they'll tell you they're not happy with our level of performances so far in the first three of four games of the season.
"You have to work your socks off for the 90 or 95 minutes and there's no doubt you have to carry a bit of luck along the way as well.
"You can defend as good as you want for the majority of the game, but they're always going to create a chance in the match given the standard of player they have.
"It's a level that everyone in the dressing room wants to be playing at and it doesn't come any bigger than playing Man United at Old Trafford.
"There's no doubt it'll be a really tough game, but we know that, if we can go out and play our game, we'll have a chance of getting a result."
Miller is almost certain to start in the lone striker's role he knows so well from his international career and from playing under Walter Smith at Ibrox.
And he is confident Rangers can produce some good football despite the cautious framework.
"The manager will obviously decide what way he wants to go and whatever he decides will be best for the team to set us out to get the right result," the former Derby and Wolves striker said.
"If he decides to go 4-5-1, it is nothing new to us as we are used to it and we played some great stuff in the majority of games in pre-season using that system."