The warning, delivered by Paul Heckingbottom ahead of the visit to Cambridgeshire, was accompanied by a series of pleas to the travelling support too - reminding them that Darren Ferguson’s side are likely to enjoy periods of pressure despite being embroiled in a battle against relegation.
United prepared for the game in 12th, 16 points above their hosts who are ranked 22nd.
But Heckingbottom said: “All games are tricky, particularly in this division. If you don’t approach any of them right then you are going to come unstuck.
“You can’t just presume you are going to get chances. You have to earn them. It’s going to be a tough game and we are going to have to be at our best.”
With only 16 outfield members of his squad taking part in Thursday’s training session at Shirecliffe, Heckingbottom wants to sign a new centre-half before Monday’s transfer deadline. Before then, however, he knows United must overcome opponents beaten 6-2 at Bramall Lane earlier this term to bolster their hopes of gaining promotion from the Championship.
“If you look at Peterborough, they have a go, they attack, especially at home,” Heckingbottom said. “Arguably that is why they are where they are, because they try and come at you rather than just sitting in - especially when they are at their own ground.”