PARIS, France - Four-times Formula 1 World champion Alain Prost has backed Red Bull's Sebastian Vettel to equal his tally of titles in 2013.Prost (58) won his championships with two teams (McLaren and Williams) over nine years but Vettel is aiming for four in a row, a feat achieved by Juan Manuel Fangio and Michael Schumacher.Only three drivers have won four or more titles since the championship started in 1950.'VETTEL TITLE FAVOURITE'Asked whether Vettel would chalk up his fourth crown, Prost replied: "Oh yes, although I hope he doesn't have a start to the season like he did two years ago when he won four or five races in a row."Vettel won five of the first six races in 2011 when he romped to his second title but he had a much tougher time in 2012, being taken down to the wire in Brazil by Ferrari's Fernando Alonso.Prost said: "He is still the favourite. Behind him, it's hard to say. 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's son Nicolas is a development driver with Lotus.Asked what conclusions he had drawn from the pre-season tests in Spain, Prost said Red Bull remains the team to beat while Hamilton's Mercedes team would be fighting to catch the other front-runners.'QUESTION MARK'He said: "Red Bull is still there and certainly better than last year at the same time. Ferrari is also good. McLaren will be certainly among the top three and Lotus also up there."There's a little question mark over Mercedes, we still don't know their level. The team was a long way away at the end of 2012 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."