FERNANDO Alonso has revealed he could be forced to leave the Enstone-based Renault F1 team if the performance of his car does not improve before the end of the season.

After leaving McLaren in acrimonious circumstances at the end of 2007 having been pipped to the drivers' title by a point by Ferrari's Kimi Raikkonen, 26-year-old Alonso knew that this year's Renault would be a step down in terms of performance.

Three races into 2008 the double world champion has a best finish of fourth place to his name, achieved at the high-attrition Australian Grand Prix.

An eighth-placed finish in Malaysia and tenth last time out in Bahrain hint at the true pace of the Renault, and Alonso concedes he could be forced to look elsewhere, with reigning constructors' champions Ferrari touted as a possible destination for 2009.

"There's a lot of things to evaluate," Alonso told El Pais newspaper.

"My first choice is to continue in Renault if we obtain a winning car and the truth is that we are advancing in this.

"But what I want is to race in a car that can give me victories.

"There are various ones - Williams, Toyota, BMW and Ferrari, of course, that are always up there whatever happens.

"I don't want to continue fighting just to get into third qualifying.

"It's hard to continue motivating myself."

Renault have promised a big step forward in performance from a heavily revised car that will make its debut at Alonso's home race in Spain this weekend, and the man from Oviedo admitted that continual revisions to the R28 chassis help him to stay positive.

"Each weekend you have something else to fuel your hope and you approach each race with that excitement," Alonso said.

"When I arrive at the Spanish Grand Prix, I will think that I can get on the podium and if not I will believe again in Monaco, because during the week you talk to the team, you know that they are working to introduce new things and, little by little, you get excited.

"Motivation remains even if the results don't come."

Alonso, who won the title in 2005 and 2006 during his first spell at Renault, added that his struggles in the first three races of 2008 have fuelled his desire to win once again.

"My priority in life right now is to win in Formula One again," he said.

"Two years ago, when I won my second world championship, perhaps I had other ideas in my head an other plans because I was winning then.

"Now that I am always behind and that I want revenge, 99% of my time I think only of returning to winning."