MELBOURNE, Australia - Red Bull's abysmal winter testing has left them lagging behind Formula 1 rivals.Double F1 World champion Mika Hakkinen said Red Bull will need at least two months to get their cars performing at optimal level.Red Bull has admitted they are playing catch-up ahead of Sunday's March 16 season-opening Australian Grand PrixHakkinen, who won back-to-back titles in 1998-99 with McLaren, would not discount Sebastian Vettel's chances of winning a fifth consecutive championship for Red Bull but said the constructors' champions were up against it.2014 FAVOURITES?Hakkinen said in an interview: "You saw in the testing they weren't able to do enough running. They haven't really got a result to the level that they want. I still think they are very far away."Bookmakers have named Mercedes as favouritesfor the 2014 title after gaining positive mileage and pace during pre-season testing - despite Lewis Hamilton's car breaking down in the first qualifying session.Mercedes said the problem was related to an oil pressure alarm triggering the engine's shutdown but conceded they had changed the car's power unit in the lead up to the session.Hakkinen said: "It definitely was a shock because every lap is so important to collect data. The regulations have changed so dramatically that the teams are having a massive challenge at the moment. There are only a few teams who are really in a stable situation."Hakkinen said it was too early to tell who would emerge front-runner after the opening round in Melbourne, but was intrigued how the new partnership of Fernando Alonso and Kimi Raikkonen would unfold at Ferrari.Hakkinen believes Williams will show signs of revival with new faces in the garage and a new driver in Brazilian Felipe Massa, who crossed over from Ferrari.He added: "Williams definitely has been developing very positively. With Massa being part of the team, it's just strengthened the whole package.Stay with Wheels24 for the first 2014 F1 race in Australia this weekend.