Tottenham landed in London on Friday morning having eased the pressure on their manager slightly with a 2-0 Europa League victory over Tromso in bitterly cold conditions.
But given that Spurs lost their last two league games - the most recent one being a 6-0 hammering at Manchester City - Villas-Boas has no time to rest, and he will be out on the training field in Enfield on Friday preparing for the visit of a United team buoyed by a 5-0 victory over Bayer Leverkusen in midweek.
Although there were positives to glean from Tottenham's display in the northern reaches of Scandinavia, the reality is that David Moyes' squad is streets ahead of what they came up against at the Alfheim Stadium.
Still, the motivation within the Spurs squad remains strong after last weekend's humiliation at the Etihad Stadium.
"We were unhappy with what we did last Sunday," Sigurdsson said.
"We have talked a lot about what happened, but that is in the past now.
"We need to get a good reaction from the squad. I am sure we will be fired up against Manchester United and we are determined to get the three points.
"We beat them at Old Trafford and drew with them at home and that can only be a positive thing for us.
"They are the team everyone wants to beat."
Roberto Soldado failed to test the Tromso goalkeeper during Thursday's win, which guaranteed Spurs top spot in Europa League Group K with one game to spare.
But the fact that Jermain Defoe and Emmanuel Adebayor were left in London suggests Villas-Boas could field his old strike partnership up front for the first time this season on Sunday.
Soldado has been in fine form from the penalty spot this term, but he has only scored one goal from open play in the league since his B£26million move from Valencia.
Sigurdsson has helped fill the void by scoring three times, but most of the others have failed to chip in like they did last term.
Only Sunderland and Crystal Palace have worse scoring records in the division so far this season, and Sigurdsson acknowledges Spurs' top-four hopes will suffer unless they address their failings in front of goal.
"Our target is to finish in the top four. We are four points off second place now so there is no need to worry yet, even though we need to score more goals than we have been doing in the last few games," he said.
"Hopefully we can continue doing what we did against Tromso and score a few goals on Sunday.
"We have to make sure we give them a harder game.
"We need to bounce back and give the club and fans what they deserve. We need to put on a performance that is more like us and we need to play attacking football, create chances and score goals and I am sure that we will do that on Sunday."
If Spurs want to learn how to sharpen their finishing then they should watch a tape of United's win in Germany on Wednesday night.
Jonny Evans, Chris Smalling, Nani and Antonio Valencia all got on the score sheet while Wayne Rooney played a part in four of the five goals inside the BayArena.
Sigurdsson watched most of the game in the comfort of his five-star hotel in Tromso, but he will be on the front line on Sunday if selected.
"Some players they have are world-class and we need to stop them, like Rooney among others," he said.
"We just have to focus on ourselves and play attacking football."
- Sports & Recreation