Ralf Rangnick says Manchester United will be fortunate to even get a point against in-form Liverpool on Tuesday if they show the same defensive frailties they did in the 3-2 win over struggling Norwich.
Interim manager Rangnick's pessimism came despite United's chances of securing Champions League football next season being boosted by defeats for rivals Arsenal and Tottenham Hotspur.
United trail Spurs -- who occupy the fourth and final Champions League spot -- by three points and have the same number of points as Arsenal, although the Gunners have a game in hand.
Rangnick fears for United's defence against a vibrant Liverpool side who reached the FA Cup final on Saturday with a 3-2 win over league title rivals Manchester City.
Jurgen Klopp's side remain on course for four trophies -- they have secured one already the League Cup -- as they are a point adrift of City in the table and in the Champions League semi-finals.
Rangnick criticised his defence for the two goals they conceded to bottom side Norwich on Saturday, saying "no other team in the league" gives away presents like that.
"Everybody has seen today's[Saturday] game and everybody knows what kind of team we are playing on Tuesday," he said.
"They (Liverpool) have just beaten Man City, they are in the cup final and they might have a chance to win four trophies this season.
"If we play like we did today[Saturday], it will be very difficult to even get a point.
"This is what we have to be realistic and aware of. We have to be lot better when the opposition is in possession."
On a more upbeat note for United was Cristiano Ronaldo's 60th career hat-trick which took him to 20 goals in all competitions this season.
It is an indictment of the contributions of his team-mates that the 37-year-old Portuguese superstar has 12 more goals than any of them.
It is the 16th season in a row that Ronaldo has scored 20 or more club goals in all competitions and moved him on to 99 career Premier League goals.
However, Ronaldo has also had moments when he has shown he is clearly unhappy with the way things are going at United and there are doubts he will see out the final year of his contract next season.
Rangnick says a decision on Ronaldo's future will be for his permanent successor, with Ajax coach Erik ten Hag reportedly likely to be appointed within days.
"In the end, this is not my decision," said Rangnick, who will stay on at Old Trafford as an advisor.
"Cristiano has another year on his contract. This will be a decision for the new manager to take together with the board.
"But he showed against Tottenham and today that he can be the difference-maker in games like this.
"It is no coincidence he has the best goalscoring record of all players in history."