With 'team orders' now legal in Formula One, Ferrari's Felipe Massa will have to raise his game right from the start of the season in Australia next week.
Only two men in very different eras, Michael Schumacher and the late Juan Manuel Fangio have won three titles or more in a row.
The Spaniard told reporters at the US Grand Prix, where he was ninth fastest in a wet first practice on Friday, that McLaren needed to find another two and a half seconds of pace to match Mercedes.
Ferrari's Fernando Alonso congratulated Red Bull's Sebastian Vettel on his fourth successive Formula One world title on Sunday but reserved judgement on where the German stood among the greats.
Fernando Alonso reiterated his long-term love and loyalty to Ferrari on Friday after McLaren, the Formula One team he left in acrimonious circumstances in 2007, said they would be keen to sign him.