Goals from Semi Ajayi and Nobel Mendy inspired the Tigers to a convincing 2-0 victory over Michael Carrick’s side at the MKM Stadium.
The result marked a new low for United, who lost their opening league game to a newly promoted side for the first time in their history.
Parker described the defeat as a “massive reality check” for his former club and believes United should now target a top six finish rather than expect another top four campaign.
“I am going to say top six for United. I think top four is going to be a struggle though,” Parker told Flashscore via RightBet when asked where he expects the Red Devils to finish in the 2026/27 Premier League campaign.
“I really do think so because of the number of games they've got and what they've gone out and got in the marketplace.
“At the end of it, they can't suffer another embarrassment, they're going to have to go into those cup games in the League Cup the FA Cup and make sure they go and do it properly.
“They can't afford to leave people out and let people go out there and let themselves down. They must compete and try and win something.
“United are further away from what they were to Arsenal last season, further away from winning the league with that performance at the weekend.”
Hull setback a reality check for United
Last term, Manchester United recovered from a difficult campaign to finish third in the Premier League, behind eventual champions Arsenal and Manchester City, and secure a place in the Champions League.
Buoyed by that impressive finish, expectations were high that Carrick’s men would overcome Hull City, who earned promotion through a controversial play-off campaign.
However, United suffered a surprise defeat, prompting the 63-year-old Parker to assess the result as Carrick’s side look to bounce back against Ipswich Town, who made a bright start in their opening game against Sunderland.
“It was embarrassing. There was nothing good about it at all. If you're Manchester United you're always looking to compete and win leagues,” he added.
“How can you still compete to win leagues when you've got two players in the team at the back in Harry Maguire and Luke Shaw? You can’t.
“The problem is that United are not prepared for winning league titles. You look at the midfield, even though they've made the signings, have they got an athletic player in that midfield? The answer at the moment is no.
“Without a shadow of a doubt, it is a massive reality check for United. Without a shadow of a doubt, it is.”
“Now, it means that the next game is even bigger because they're at home to another newly promoted side, one that was there 12 months earlier, and United simply have to go out and prove themselves.
“The difference is that Ipswich won their first game at home, whereas they lost their first game at home to Liverpool at Ipswich last time they were in the Premier League.
“They've won their first game and they're in a great position to come to Old Trafford on the back of United playing poorly.
“Hull City used Manchester United's games over pre-season to set themselves up in a fashion to try and beat them from what they’ve seen, which they've done.
“Ipswich are going to be no different. Gary O'Neill is a very studious fella, and he'll be back-flipping and everything if he was to win at Old Trafford with Ipswich."
Maguire has no place in United’s future
Parker also urged Manchester United to move on from Maguire, insisting the experienced centre-back should not be part of their plans as they look to challenge for major honours.
The England international partnered teenager Ayden Heaven at the heart of the Red Devils’ defence, but endured a difficult afternoon against Sergej Jakirovic’s side.
Maguire finished the game with no tackles or interceptions as the 13-time Premier League winners struggled to contain their opponents.
The 33-year-old came under further scrutiny after appearing to wrestle with his own team-mate Noussair Mazraoui in the build-up to Nigeria international Semi Ajayi’s opening goal, with Maguire expected to be tracking the Hull defender.
Parker believes United must prioritise the development of their younger players while bringing in quality reinforcements capable of helping the club compete for major trophies.
“I just think it's madness (that Maguire continues to start at Manchester United),” he stated.
“You've got young players there and you start trying to move forward and start trying to introduce players who are going to take you towards possibly win a title, and then you might just make that one big sign and then it clicks.
“But Harry Maguire has been there through all the poor times and he's got a few trophies, but they're not the big ones.
“United are about the big ones and they'll be nowhere near the big ones whilst he’s about.
“So, they need to start looking beyond him, and for him to start the season, I think that tells you that they’ve got it completely wrong. For him to start the season, I just don't think it's right. They need to move forward.”
Manchester United welcome Ipswich Town to Old Trafford on Sunday looking to put their shock defeat to Hull City behind them.
The Red Devils will be favourites to claim all three points, having won each of their last five home meetings with the Tractor Boys.
