Daniel Ricciardo still thinks Mercedes are the team to beat in 2018 despite the Aussie setting a new track record at the Circuit de Catalunya.
Ricciardo was the star of the show on day two of the second test as he lit up the timesheets with a blistering time of 1:18.047 on hypersoft tyres.
However, even though the time added further evidence that Red Bull could be in a position to attack from the off this season, Ricciardo believes Mercedes are still playing their cards very close to their chest.
"I'm sure Mercedes are still the top dogs at the moment but I don't feel we are far off," said Ricciardo. "If we can keep finding a few more things we can be very good."
"We will find out in Melbourne but while I think Mercedes still have a bit on us I don't think it's too much.
"We seem to be close. Ferrari, l would guess, are close too. I think we are similar to them."
Ricciardo also pointed out that Mercedes have yet to join them by setting their best time on the quickest tyre available: the hypersoft.
He added: "Mercedes seem to be quickest at the moment – if they used the hypersofts l think they would be a few tenths up the road.
"If they are, we can definitely find that quite soon and don't let them win five in a row!"
Ricciardo is due to return to action for the final day of testing on Friday.