Prost said he believed the German Red Bull driver, who has won the past three F1 championships, was the firm favourite for the 2013 title.
If Vettel wins in 2013, he would create history, with only Argentine great Juan Manuel Fangio and Ferrari legend Michael Schumacher having won four consecutive F1 crowns.
“He is still the favourite. Behind him, it’s hard to say,” said Prost.
“Will losing (Lewis) Hamilton and having a young driver in his place be destabilising (for McLaren)? Mercedes will not be challenging for the title, I don’t think so.
“Alonso could be the most dangerous behind Vettel and why not an outsider like (Lotus’s Kimi) Raikkonen or (Romain) Grosjean?”
Prost also said he believed Red Bull were the leading constructors, and likely to set the standard.
“Red Bull are still there and certainly better than last year at the same time,” he said.
“There’s a little question mark over Mercedes, we still don’t know their level. They were a long way away at the end of last season so I don’t see them suddenly returning to the front. But they will be up there at certain tracks.
“It could be a very even field, we’ll see some good races.”