Cavani dropped into the free agency pool at the end of June after failing to agree on a contract extension with Paris Saint-Germain.
The 33-year-old established himself as one of the top strikers in world football during his time at Parc des Princes, scoring 200 goals in 301 outings for the French giants.
The arrival of Mauro Icardi last summer saw Cavani pushed down the squad pecking order, but he still left the club with 21 major trophies to his name, including six Ligue 1 titles.
The likes of Atletico Madrid, Inter and newly-promoted Premier League outfit Leeds United have all been linked with the Uruguayan in recent weeks, and a possible return to South America has also been mooted for the veteran forward.
However, Benfica look set to win the race for his signature, with Cavani confirming earlier this week that he has held talks with the Portuguese club.
Saha cannot understand why United haven't made a move for Cavani, with it his belief that Ole Gunnar Solskjaer's current squad is still lacking a natural number nine.
"I think Manchester United are missing a trick by not signing Edinson Cavani this summer," the former Red Devils star told the Football Index Podcast.
"I’ve followed him for many years and I’m gutted there doesn’t seem to be an interest there. For me, Cavani would be the best fit this summer.
"Cavani has a great eye for goal and his leadership would be a great asset. He has qualities that are very difficult to find on the transfer market."
Saha went on to suggest that Lyon's Moussa Dembele could be a good alternative option for Solskjaer as he looks to bolster his attacking ranks.
The Frenchman is certain that Dembele, who came off the bench to score twice in Lyon's 3-1 Champions League quarter-final win over Manchester City last weekend, could add a new dimension to United's line-up due to his physicality.
"I think Moussa Dembele could be an interesting signing for Manchester United," said Saha.
"I know from my time at Fulham that Dembele is physically strong and he would be a very good target man.
"He would be able to hold up the play and bring wide players into the game as an effective plan B against some opposition."