In an interview with Lusa, the former French player understands that the Old Trafford club has gone through a "transition phase that is never easy" after their last Premier League title in the 2012/13 season.
However, he believes that the team he represented between 2003 and 2008 has failed in its choice of players and coaches and is experiencing a "real crisis", which he wants to see solved by the 40-year-old Portuguese coach.
"We're talking about a great club that deserves better. I think they have the right coach to do the surgery they need. It won't be easy. If he has the right players, he can do an excellent job," Saha emphasised from a training camp for children and young people at the Pine Cliffs Resort in the Algarve town of Albufeira.
The scorer of 42 goals in 124 games for the Red Devils, who won the league 13 times between 1992/93 and 2012/13 before their current slump, Saha admits that it was "painful" to watch United finish 15th last season - their worst finish since 1973/74, when they finished 21st and were relegated to the second tier.
Linked to the English club since November 2024, after four-and-a-half years at Sporting, Ruben Amorim is, for Saha, a coach who stands out for his communication skills, honesty and "very well-defined ideas about how to play".
"He needs to rectify some mistakes made last year and realise that nothing will be easy. He's also willing to improve, as are the players. If he grows together with the players, he'll be successful," predicts the former footballer, now 46.
Bruno Fernandes has done 'a fantastic job'
Although he considers it important to qualify for UEFA competitions next season and to adopt "a style of play understood by all the players in the squad", the former France international believes that the Portuguese's main mission is to make the club "respected and feared" again, especially as the home side.
"Any team that goes to Manchester must think that they're facing a difficult game. I see mid-table teams convinced they're going to beat United, with so many mistakes on the pitch, so many controversies in the press.
"Manchester United must once again guarantee the basics - to be respected and feared. At the very least, Old Trafford must once again become a graveyard for other teams," he emphasised.
Although Saha sees the Premier League as the "most difficult league in the world", with seven teams capable of "reaching the top", the former forward believes that United can and must "find a balance" to get closer to the time when they dominated English football, with Sir Alex Ferguson at the helm.
Saha recalls that the Scottish manager, now 83, "knew every player he chose in depth, their families, their problems, their weaknesses, their strengths" and that, in those days, "everything worked like a symphony" in Manchester, both on and off the pitch.
Disgruntled by "some bad signings" in recent years and cases of players "being paid far more than they should, earning star status too soon", the Frenchman believes that Portuguese international Bruno Fernandes has performed admirably as a midfielder and captain, having to cover up weaknesses that the captains of the club's glory years were not subject to.
"The pressure Bruno has been under in recent seasons has been too much. Any weakness is immediately pointed out. Captains like Roy Keane didn't have the challenges he has because Manchester United were a winning team on the pitch.
"There weren't these crises of confidence. To ask a captain to do something that other United captains never had to do is unfair."
Even if there is room for improvement, Saha emphasises that the 30-year-old Portuguese has carried the burden in terms of output for the side, scoring 98 goals and registering 84 assists in six seasons, and must "remain true to himself to lead" the Red Devils in 2025/26.
The former United striker also believes that right-back Diogo Dalot can "help the team offensively" in the coming season if he is "surrounded by confident players", not least because he had a "very successful" 2023/24 season before experiencing a tough period last season.