Manchester City boss Manuel Pellegrini claims rivals United have a squad close in quality to his.
At times during the season the clubs have seemed to be heading in opposite directions but Pellegrini, guarding against complacency, has warned there is little to choose between them.
The two sides clash in a derby that could have big implications for both of their Champions League ambitions at the Etihad Stadium on Sunday (4pm).
City have reason to be wary, having fallen off the pace in the Premier League title race and been dragged into a fight for their top-four place.
United, after a turbulent campaign, are hoping to mount a late charge to break into those Champions League places.
Pellegrini said: "I think they are very close, both squads. Both of them, they have good players. United have also invested a lot of money to try to improve their squad.
"United have a very good squad. It doesn't matter which players play, or in which way they play, they are always a dangerous team."
Pellegrini still has ambitions beyond the top four - and is not ruling his side out of title contention - but is well aware of the importance of this fixture in terms of securing Champions League football for next season.
With victory City can deal a blow to United's outside chances of overhauling them but losing could leave the club - who are preparing to welcome Pep Guardiola as new manager in the summer - living on their nerves.
Pellegrini said: "It's a game of six points. That would make an important difference but it's not finished after that. There are 21 more points to to play for so you never know what will happen."
City will have to overcome the loss of captain Vincent Kompany, who faces at least a month out with the calf injury suffered against Dynamo Kiev in midweek. Nicolas Otamendi, who left the field with a dead leg in the same game, is hopeful of recovering in time to feature.
Meanwhile, Marouane Fellaini admits missing out on Champions League qualification would be unacceptable for United.
The pressure is cranking up on Louis van Gaal as a difficult campaign edges towards completion, with the Dutchman's side lagging four points behind in the race for a top-four finish.
The under-fire United boss accepts their Champions League hopes could all but be extinguished if they lose at fourth-placed Manchester City.
Thursday's Europa League exit to Liverpool means the Premier League is their only remaining route to the continent's top table - a finish Fellaini believes is the bare minimum.
"We have to do it because a team like Man United have to be in the Champions League next season," he told the BBC. "We will fight to the end to be there.
"The derby is a great sensation, (a great) atmosphere. All the city will watch the game - the challenge, goals, everything - because it will be a big game, so everyone likes to watch a game like that."
United supporters will not hold back if their side falter at the Etihad Stadium, if this campaign is anything to go by.
Van Gaal is not the only target of their ire as for some Fellaini is symbolic of the club's decline in recent years, with his substitution in last weekend's FA Cup quarter-final against West Ham cheered by pockets of supporters at Old Trafford.
"I think the players are used to it," he said of the criticism. "I don't read, I don't listen. I am just focusing on my job. Okay, sometimes it is hard for my family, but the rest I don't look at it."
It is not just Fellaini's footballing style that has been criticised as former referee Howard Webb branded him a "thug" for his physical approach in the Europa League last-16 clash with Liverpool.
In the first leg at Anfield he appeared to elbow Emre Can - though avoided any action from UEFA - and then in Thursday's return was booked for making contact with Dejan Lovren with a flailing arm.
"I don't want to elbow someone, I just defend myself," Fellaini said. "Okay, I am physical, I like to win my challenge - that's English football as well - but I am not a dirty player."
When Webb's "thug" criticism was put to him, Fellaini added: "Yes, it's strong but I choose to defend myself, like I said.
"I like to win my challenge when I play a game. In England, it is everything with a lot of physical challenge. If you want to win the game, you have to be aggressive, you have to win your challenge.
"I never want to injure a player or to be bad. No, I am not like that, I just defend myself."
Jose Mourinho's continued unemployment and desire to return to the dugout this summer has cast a shadow over Van Gaal, even if the Dutchman continues to brush questions about his future aside.
Fellaini was brought to the club by predecessor David Moyes, but appears to have affection for the man currently in charge at United.
"Of course it's easier, I knew him for five years or six years," he said about former Everton boss Moyes. "I knew his stuff, I knew his mood, I know everything.
"So, yes, (it was easier) but it is a good experience as well with Van Gaal. I think he's a good man, honest, he loves football so he tries do everything for the club."
