Mercedes expects midfield Formula 1 teams to surprise in 2019

Ferrari is currently believed to be the team to beat following its encouraging performance at Barcelona, but behind it things are much harder to work out.

Wolff - whose drivers Valtteri Bottas and Lewis Hamilton ended the first test sixth and seventh on the combined timesheets - said as well as the order looking tight at the front, several midfield teams had caught the eye.

When asked who he expected Ferrari's main competitor to be, Wolff replied: "I see everybody. There could be Red Bull for sure. It has the resource to be competitive, and it has always been a flexible team to adapt to new regulations, and even change directions.

"Ferrari has just got stronger and stronger and stronger. Then Renault was the quickest team on the last few days. Toro Rosso was unbelievable, Alfa Romeo was very good.

"So all of them; there could be a situation where we are all very close together and there could be surprises."

Reigning world champion Hamilton reckoned the clear advantage the top three teams have enjoyed over the rest of the pack in previous seasons was no longer guaranteed.

Asked about who he thought would be battling for the championship, the Mercedes driver said: "I think at the moment you can't rule out anybody.

"There are at least six drivers at the moment that can have the potential performance wise to fight. We just have to watch the development.

"At the moment when we do testing I don't look at what anyone else is doing, I just look at my data and my understanding of what is happening with the car and the tyres, and that is all we can do.

"At the moment everyone is doing a different programme but I hope it is at least us three teams - and maybe Renault can come along, who knows?"

Renault's Daniel Ricciardo, whose team-mate Nico Hulkenberg set the fastest time of the first week of testing, felt every team had impressed so far.

"I kind of feel that everyone has a pretty decent car at the moment," he said.

"So to be in the 1m17s, even the 1m18s, you are kind of humming: Turn 3 would be flat, Turn 9 would be flat. The cars are probably not doing that much wrong, so it is hard to pick it."