The Serbia international is among those reported to be figuring on the Red Devils’ transfer radar as they prepare to make additions in the summer window.
Former Lazio striker Casiraghi told RMC Sport on the mounting transfer talk: "I do not know if the valuation is right, if I had €100m I would buy him.
"I like him very much, not just from today, he was immediately seen as a great player.
"He is unique, he is [just] 23 years old."
Casiraghi, who spent five productive years in Rome during his playing days, is not the only former Lazio star to have come out in support of Milinkovic-Savic making a big-money switch.
Stefano Fiore has also suggested that the highly-rated Serb can be a bargain for somebody, with €100m no longer an obscene asking price in an inflated market.
He said: "Given the figures that are now involved in football, he is worth the money because of the quality and characteristics he possesses.
"I also watch a lot of foreign football but players like him are not there.
"An auction will open and we'll see what happens, but if a defender can go for €70m [£61m] in England then Milinkovic-Savic is worth much more.
"That said, the market has gone crazy and should return to more normal figures."