By SABC Sport
11th September 2024
The Portugal star fell out with Ten Hag before his second spell at Old Trafford ended in 2022.
Ronaldo, who plays for Al Nassr in Saudi Arabia, believes his former club need to "rebuild from the bottom" but should not rule out winning major trophies in the meantime.
Ten Hag has said he is "quite confident" of claiming further silverware this campaign after lifting the Carabao Cup and FA Cup during the past two seasons.
But the Dutchman has also regularly downplayed the extent of what can currently be achieved, saying in July his team are a "long way away" from being ready to win the Premier League.
"Manchester, they need to rebuild everything, in my opinion," Ronaldo said in an episode of the Rio Ferdinand Presents podcast due to be released on Thursday.
"The coach, they say they cannot compete to win the league and Champions League. Manchester United coach, you cannot say that you're not going to fight to win the league or Champions League.
"You have to be, to mentally say, listen, maybe we don't have that potential, but I cannot say that. We're going to try. You have to try."
Ineos founder Sir Jim Ratcliffe in February bought a 27.7 per cent stake in United, who have not won the title since the departure of Sir Alex Ferguson in 2013.
Despite upsetting Manchester City in the FA Cup final in May, the club endured their worst Premier League campaign last term, finishing eighth on 60 points.
The 20-time English champions began the new season with a 1-0 win over Fulham before suffering back-to-back defeats to Brighton and Liverpool ahead of the international break.
"This club needs time to rebuild because it's still one of the best clubs in the world, but they need to change," Ronaldo said.
"They understand that. This is the only way. This is why they show, they start to change again, the structure of the club, the president, the infrastructures and everything. The owners of the club.
"I believe that the future will be bright. I believe, but they don't depend only on the talents. It's more than that. It's all club, all, not only players, club, everything as a unit, united.
"They have to rebuild from the bottom. If not, they cannot compete. It will be impossible.
"They can do good things, yes, they can win Carabao, yeah, but I mean, Champions League or Europa League or Premier League, difficult, in my opinion. And I wish that I'm wrong, I wish, but will be difficult."
Five-time Ballon d'Or winner Ronaldo scored 27 goals in 54 appearances during his second spell with United after signing from Juventus in 2021.
Following his exit just over a year later, he claimed to feel "betrayed", while saying of Ten Hag: "I don't have respect for him because he doesn't show respect for me."
However, the 39-year-old said he still loves the club.
"I'm not happy the way it all happen, but in the same way, we cannot control some points of our life sometimes, but it's done, already done," he said.
"To prove that I'm right or wrong, this is not my issue any more. I say what I have to say and for me it's done.
"But to be honest with you, what I wish for Manchester, it's what I wish for me. The best they can make, again the best team they can, and I love that club. I'm not that kind of guy that forgot the past."