The Portuguese star began his career at the club, alongside the world's most expensive player Cristiano Ronaldo.
Asked who United should buy, Nani said: "I'd have some young players, Miguel Veloso and Yannick Djalo.
"They are very good players I knew from Sporting."
Striker Djalo's last-minute goal against Brondby in August helped Sporting reach the Europa League group stage with a 3-2 aggregate win.
Veloso, also 24, taunted Everton from midfield in last season's Europa League, scoring in both legs of the 4-2 aggregate win against David Moyes' team in the last 32.
He left Sporting in the summer to join Genoa in Serie A in a £7.5million deal.
Nani, who cost United £14m in 2007, has no doubts that the Premier League is the place to be.
And he would recommend it in a heartbeat to Veloso and Djalo. He said: "I played in Portugal and I watch different leagues. But I think the best league is in England."