Rubens Barrichello [Images] could have been Formula One world champion twice over with Ferrari [Images] had Michael Schumacher [Images] not been his team mate, according to technical director Ross Brawn [Images].

The Briton expressed his disappointment on Friday that the Brazilian, who has yet to win a title, had decided to leave Ferrari for Honda-powered rivals BAR at the end of the season.

"We are very disappointed because we've had a very good period with Rubens and I've said many times he has the toughest job in Formula One," said Brawn at the Turkish Grand Prix [Images].

"He's trying to beat Michael Schumacher in the same equipment and nobody's ever managed to do that. It can be a very frustrating experience and he's always tried hard and worked hard and done a very good job.

"I was disappointed with what happened but I can understand why it happened."

Barrichello joined Ferrari in 2000 and was runner-up to Schumacher in 2002 and 2004. The German, now a seven times champion, has won the title every year the Brazilian has been at the team.

Barrichello said that one of his better moments at the team was strangely the 2002 Austrian Grand Prix where he was ordered to move over for Schumacher after leading from the start to the final corner.

That call triggered worldwide outrage and led to the governing body banning such 'team orders'.

"I think that was the best time because they [Ferrari] knew I could win races without the help of anyone, so it was probably the turning point of my racing career there," said Barrichello.

Brawn begged to differ on that.

"Obviously Rubens perceived something within the team. I didn't see it because I took him as a serious racer all the time so there was no change from our side.

"He would have been world champion if Michael Schumacher hadn't been there. Once, maybe twice. That's, to me, the standing of Rubens. He's been doing a great job and getting better each year," said Brawn.

The technical director also said that Barrichello's decision to leave meant the driver would be doing less testing for Ferrari for the remainder of the season.

"I think there is some testing he won't do. Obviously new car things, V8s, items like that it wouldn't be sensible for him to do," he said.

"But he's going to the Monza test [next week] and I think there will be one or two tests he will do before the end of the season...but it will be very specific 2005 work."

• Formula One coverage