Jenson Button has said he views Fernando Alonso as the man who will be the biggest challenger to Sebastian Vettel in the race for the 2013 F1 title.
Vettel took his fifth win of the year in Belgium at the weekend to extend his championship lead to 46 points, with Alonso sitting second in the standings having finished as runner-up to the Red Bull man at Spa.
Double champion Alonso has won on two occasions this season, although the second of those came all the way back in May when the Spaniard took victory in his home event in Barcelona.
While Mercedes currently sit second to Red Bull in the constructors' championship, McLaren ace Button said he felt it was Alonso and Ferrari who could become the biggest rival to Vettel for the crown.
"I think Fernando's the one to look at to challenge Sebastian,” he told the Guardian
. “He seems happy with the car and they're making progress.
"I think Ferrari will be strong at Monza and have a very good chance of winning there. They're stronger now than this time last year and could do very well. The championship's not over."
While Button put his backing behind Alonso, his former McLaren team-mate Lewis Hamilton said he was confident that Mercedes was still very much in the mix.
"Already this year has been a major success, third in championship, second in constructors' championship,” he said. “We can't be disappointed with where we are for the rest of year. But we're hungry to win.
"It's within arm's length so we just have to keep pushing and hope that when we get to those high downforce circuits we have more of a chance.
"[However] Seb was rapid [in Belgium] and he could win way before the end of the season."