Manchester United need to sign more world-class players if they want to compete in the Premier League and Europe, according to Nani.
United are facing a big off-season after failing to qualify for the Champions League, having finished sixth and 32 points adrift of winners Manchester City in 2018-19.
Ander Herrera and Antonio Valencia have already confirmed their Old Trafford departures, while the futures of Paul Pogba, Romelu Lukaku, Alexis Sanchez, David de Gea and Juan Mata are uncertain.
United have been linked with Ajax captain Matthijs de Ligt, Benfica sensation Joao Felix, Real Madrid outcast Gareth Bale and Paris Saint-Germain full-back Thomas Meunier as Ole Gunnar Solskjaer tries to rebuild his squad.
Nani was part of the last United team to win the Premier League in 2012-13 and the Portuguese star has been left saddened by the club's struggles.
"United need more world-class players. Change something, attitude on the pitch," Nani – who plays for Orlando City in MLS – told Omnisport.
"I remember from my time with [former manager] Alex Ferguson, a lot of games we weren't playing our best, we weren't playing beautiful football but in 15 minutes we played with our hearts and to score goals.
"We run, fight for each ball. That's the way we get all the results. They must have more desire to win every battle on the pitch, every ball, every challenge because just like that they're going to improve."
Nani, who won four Premier League titles and the Champions League among other trophies before leaving United permanently in 2015, added: "It's hard to do well when the past is still there. All the big names and important people who made the club achieve so many trophies, they left.
"Now, most of them are still around but not doing what they were doing in the past like coaching or playing. Now, they need to build a new strong team, a new strong mentality. This takes time. This has been the problem at Manchester United at the moment."
"I keep track. It makes me sad for the club, the players. It's not the moment of United. Maybe for next season they can do much better," the 32-year-old continued.
"As a team, they are not a strong team. They must know that. Obviously, it's still a young team too and maybe the club need to sign some top, experienced players to keep United among the best clubs in the world, with Barcelona, Real Madrid, Chelsea, Manchester City and Liverpool.
"Because at the moment, we can't compete with them because they are stronger. But in one season, everything can change."
Solskjaer replaced Jose Mourinho in December and the club favorite's interim appointment sparked a rejuvenation as United stunned PSG to reach the Champions League quarter-finals.
However, United only won two of their last 12 matches in all competitions – the Red Devils ending the Premier League without a victory in five games – as Solskjaer signed a permanent three-year deal.
"He's been there in the past," Nani said when asked if Solskjaer can lead United back to glory. "Obviously he has a different role now but he knows the mentality and how the club achieved what they have.
"But he has some good stuff to show the players, to change the mentality, to take them on the right way to fight for all the competitions. And try to be as quick as possible, the old United."