Sir Jackie Stewart believes that Heikki Kovalainen's form could be crucial in helping Lewis Hamilton as he bids to win the 2008 F1 drivers' title.

Stewart reckons that Kovalainen needs to do more to take points off the likes of Felipe Massa and Kimi Raikkonen - and that if he doesn't improve it could end up costing Hamilton and McLaren-Mercedes.

Speaking to British tabloid newspaper, The Mirror, the three-time world champion added that Ron Dennis' men need both of its drivers battling at the top if they are to succeed.

"The way the season is panning out it is going to be nip and tuck for the drivers' championship right to the end of the season. Lewis has to be well supported by his team-mate," Stewart explained.

"Kovalainen has got to be able take a position away from a Ferrari driver. You can't have a one driver team in this sport.

"Lewis and Kovalainen have got to keep finishing. In Lewis' case it's a simple fact that no-one wins all of the time. But it's no good winning well and then not finishing the next race."

Stewart's comments follow those made recently by McLaren-Mercedes CEO Martin Whitmarsh, who noted that they need to do more to help Heikki realise his full potential.

"Firstly, let's not forget that Heikki is a brilliant racing driver. His pass of Robert Kubica at Hockenheim reminded anybody who needed reminding that he has all the speed and skill to be battling at the front. But there's no magic in Formula 1 and we still need to work with Heikki to extract his full potential," Whitmarsh added.

"At Hockenheim, he didn't get the best out of himself or the package and we need to work on how we fine-tune the car's set-up and how Heikki is involved in that process.

"He was at MTC on Tuesday to carry out his pre-race programme and is working hard with his engineers to find a set-up that allows him to maintain his speed throughout a race stint without suffering from some of the rear-end nervousness he has encountered in recent races."