Felipe Massa has questioned whether Williams is using the same Mercedes engine as the factory team, claiming the gap to the front during the Australian Grand Prix is 'too big' to not raise suspicion.

The Brazilian started as 'best of the rest' in third place behind the dominant Mercedes' of Lewis Hamilton and Nico Rosberg, but while he held position from the start-line, he could not keep Sebastian Vettel in the Ferrari behind him through the pit-stops.

Going on to finish in fourth place, though Massa blamed time lost behind Daniel Ricciardo on his out-lap for losing out to Vettel, he nonetheless admits he is worried his Williams team is not receiving the same quality Mercedes engine as the factory team.

"We're pushing hard with the engine which I'm sure has some improvements that we can have and are pushing to have, because for sure the difference is too big. So I really hope that we really have the same engine, which I really don't see why we don't have."

Indeed, Massa had joked in the post-qualifying press conference - alongside Hamilton and Rosberg - that the large gap to the front is surely down to the chassis if the engine is the same, saying: "If we have the same engine the difference should be in the car, or... I hope we have the same engine. I believe we have the same engine."

However, Massa furthered this train of thought after the race, questioning why Mercedes would want to 'help Ferrari' by not giving Williams the best power unit it can supply.

"Why would Mercedes help Ferrari? So we need to have the best they can give, and we will work on that. On the car we know that every race and whatever points you're not getting, it counts.

"[Last year] For sure we improved massively from the first race to the last race and the engine improved a lot. If we don't have the same engine - which I cannot say 100 per cent because it's very difficult to say - but if we don't have it then we want to have it because it's not nice that we don't have it."