REUTERS: Lewis Hamilton suspects Red Bull may have the fastest car on the Formula One starting grid at next week's Australian season-opener.
Mercedes' four times world champion, who remains the bookmakers' favourite for a fifth title, told reporters on Wednesday that Red Bull could be the team to watch come Melbourne on March 25.
"I think Red Bull are the fastest at the moment, potentially," he said at an event for title sponsor and fuel partner Petronas in Turin, Italy.
"They have some sort of upgrade coming, of some magnitude, two-to-four tenths (of a second) or something like that. That's what I heard," added the Briton.
Ferrari set the fastest laps in pre-season practice but most analysts of those sessions saw Mercedes as still ahead with former champions Red Bull possibly their closest competitors.
Both Mercedes and Red Bull were focussing more on long runs and reliability than performance in Barcelona.
Australian Daniel Ricciardo and Dutch 20-year-old Max Verstappen won three races between them last year to Mercedes' 12 but finished the season strongly.
Red Bull team boss Christian Horner has said he still sees Mercedes as favourites, however.
"I think this year is going to be exciting, because last year there was a big difference between teams in the beginning, and then they got closer," said Hamilton, who triumphed in nine races in 2017 after Ferrari won the opener.
"But this year I think it starts this close and then it's going to overlap, and separate, and overlap during the year, as people are developing."
Hamilton said he had still to sign a new contract but remained hopeful it could be done before Melbourne. The 33-year-old is out of contract at the end of the year but both parties have said they want to extend.
(Reporting by Alan Baldwin in London, editing by Toby Davis)