Sebastian Vettel says it is 'only a matter of time' until his former team Red Bull are back up to speed and probably challenging Ferrari and Williams for podiums behind Mercedes.

Following an impressive debut performance with the Scuderia in Australia, Vettel comes to the second round in Sepang for the Malaysian Grand Prix hoping to make in-roads into Mercedes' substantial advantage and establish a gap behind to closest rivals Williams.

However, Vettel says he expects Red Bull to factoring in their battle soon enough despite its current spat with Renault over reliability and performance.

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"I think the favourites are very clear - just look at the gap from Australia - and then after that I think it will be very close. For us we try to confirm the result and the impression we left in Australia, so we try to make sure we establish ourselves in a similar position, ideally a little bit closer to Mercedes and a little bit further away from Williams.

"I expect it to be very close between us and Williams, and also I think Red Bull is a question of time until they come back. Obviously now they are struggling a bit so I think behind Mercedes it is very close."

Having taken the Red Bull-Renault combination to four world titles between 2010 and 2013, Vettel firmly believes the professionalism of both parties will see it make strides forward soon enough.

"In the end I'm not there anymore so I can't judge what is going on. I can only see what everyone else can see and hear. It's never nice when you use the public to have whatever kind of debate.

"I know that both sides are very professional; I know the chassis side in Milton Keynes but also the engine side in Viry so I'm sure they're probably not where they want to be but they are a strong competitor and they will probably come back."