United are strong favourites to win having climbed into fourth spot in the table with a string of impressive results recently.
But McNamara insists his team will not take their visitors from Edinburgh lightly.
McNamara said: "Hearts are coming off the back off a heavy defeat.
"This will make it hard for us because they will be wanting to get that out of their system.
"This will not be an easy game by any standards.
"We know Hearts still have a lot of good players who want to do well this season.
"So we know we'll have to try and reach the levels of performance that we have been in recent weeks."
United defender Gavin Gunning could miss out due to a knee injury which has been troubling him in recent weeks.
Winger Gary Mackay-Steven is hoping to shake off a groin injury in time to face Hearts.
Nadir Ciftci is unavailable after the SFA handed him an automatic one-match ban earlier in the week in the wake of last month's League Cup match against Inverness.
Skipper Danny Wilson insists his Hearts team are not scared about receiving another painful drubbing.
The Gorgie outfit shipped seven goals to holders Celtic as they were knocked out of the William Hill Scottish Cup.
That excruciating drubbing followed punitive punishments dished out to the administration-hit Jambos, which mean Gary Locke is banned from signing new players, leaving him to work with a squad whose average age is just 22.
But defender Wilson - who will lead the side out against Scottish Premiership rivals United at Tannadice - insists their display against the Hoops has not left them worried about future beatings.
He said: "We can't go in fearing another result like that. If you do then there is no point turning up.
"The most important thing is that we learn from it. We have seen the mistakes we have made - now we need to eradicate them from our performances.
"But we don't go into any game fearing a hammering. We go in hoping to win. It was the same on Sunday but it didn't happen. Now we just need to move on."
The Tynecastle men will finally return to zero points with a win on Tayside - six months after they were fined 15 points for breaking insolvency rules.
Before turning his attention to Jackie McNamara's side, though, Hearts manager Gary Locke forced his squad to sit through a re-run of Sunday's defeat.
While it was uncomfortable viewing, former Liverpool centre-half Wilson insists it was educational.
He said: "We can't erase last weeks game from our minds. As bad as it was and as embarrassing as it was, you have to try and learn from every experience.
"We came in on Monday and went through the game, trying to see where we could have done better. Celtic may have been exceptional but we were nowhere near where we should have been.
"Was there a fear coming in on Monday to watch it again? Yeah, there probably was because we had lived through it once. We didn't want to do it again.
"We sat there and discussed it. Some people aired their views but the video footage didn't lie and it was clear we were lacking in a lot of places.
"But I think the young lads will be fine. They have played the majority of the season and have performed well. Hopefully we can just put that down as a bad day at the office."