United allowed both Romelu Lukaku and Alexis Sanchez to join Inter - on permanent and loan deals respectively - in the latest transfer window, leaving Marcus Rashford and Anthony Martial as Ole Gunnar Solskjaer's only senior striking options.
Rashford has been in patchy form, scoring four goals from nine league appearances, while Martial has missed the majority of the campaign so far due to injury, with teenager Mason Greenwood called on at times to lead United's line.
Though Martial is now back to fitness, United's issues up front have been a source of debate, with the club's former captain Roy Keane suggesting Tottenham's Harry Kane should be a priority target.
Saha says PSG and France star Mbappe is a player United should be looking to purchase, but he knows they may have already missed their chance.
"If you ask me, I would break the bank for Mbappe, but now it's too late," Saha told Compare.Bet.
"But, when you look at strikers, it's a dying breed. [Robert] Lewandowski is a rare example of someone who is left, and I don't see many players that can easily fit up front.
"I had views on some strikers like [Atalanta's] Duvan Zapata who I think is a decent player, very strong.
"There is a need for somebody up front who is strong enough to hold the ball and to give time and space to the players like Paul Pogba and [Scott] McTominay to create something in midfield to put passes together."
Saha also believes the style of play employed by Solskjaer has often been "too nice" for United's own good.
"You're asking a lot from young players because passing the ball around and having nice touches, it just looks too nice and it doesn't work," Saha added.
"This football is really down to possession, but hard on young players especially when they don't have confidence.
"You need a couple of big strong characters to talk to people, to do the dirty jobs, winning duels, and to help the fans react. I think that's what we want to see.
"When we lose we have that challenge that nobody likes. Passing is nice but you don't hurt anybody."