Manchester United Treble-winner Nicky Butt has said his old club risk applying a "sticking plaster over a gaping wound" to keep pace with a Manchester City team he believes can become the second English club to achieve the Treble.
City are now on course to emulate Sir Alex Ferguson's 1999 team by winning the Premier League, FA Cup and Champions League following Wednesday's 4-1 win against Arsenal, which puts the reigning champions in control of the title race.
Guardiola's side also face Real Madrid in the Champions League semifinals and have an FA Cup final clash against United at Wembley on June 3 as they attempt to match the feats of Ferguson's greatest team.
Butt, who is chief executive at League Two side Salford City, said City are good enough to join United in the history books this season.
"They [City] are an amazing football team," Butt told ESPN. "Whoever wins the Treble, I'll be a bit gutted about it, but if they're doing it in the right way, playing the right way, then fair play to them.
"The project that they've had over the last 15 years, from when they took over, they have changed all the fundamentals in the local area.
"The owners are putting money into the local community, building houses. I'm the biggest Red you'll ever meet, but you can never say it's not an amazing project that they have put together.
"They brought in a manager that's certainly in the top three ever in my opinion, and they're playing unbelievable football. They're probably going to win the title, they're into the FA Cup final against United and they're looking good in the Champions League, so you'd have to say they've got a real chance of winning all three.
"The way they play football and what they do, you can't not say they're good. They're very, very good. What they did against Bayern Munich in the Champions League was frightening really.
"To go and do what they did there is phenomenal. So if they win it, well done. Good luck to them, but I don't think they'll do it in a style we did it in."
Erik ten Hag's United team can still wreck City's Treble bid by winning the FA Cup in the first-ever all-Manchester final in June.
However Butt, who made 47 appearances in all competitions during United's 1998-98 Treble-winning season, said United are still a long way behind City in terms of competing for the top honours.
"It saddens me, yeah, because I still think they [City] are streets behind United as a historical club, as a club, they're catching up fast, let's be honest," Butt said. "The infrastructure that they've built will see them through for the next 20 or 30 years.
- The VAR Review: John Stones offside, Thiago handball penalty
- Ogden: Only Man Utd, Madrid can stop City winning the Treble
"I think the biggest thing for United now, whether the owners stay or new owners come in, is that they have to fundamentally look at the foundations of the club.
"Because there's no point buying a Harry Kane and then saying that's going to do us for four years because it's just a sticking plaster over a gaping wound.
"And the gaping wounds are they're because, fundamentally, there has to be an infrastructure put in place where they can have a base to work from.
"I think Ten Hag is an amazing coach. I think he'll do unbelievable stuff at the club if he's backed, but it's really difficult attracting top, top players if you haven't got the fundamentals of a football club right.
"Unless you've been attracting the wrong players who'll just come for money, which has happened over the last five or six years."