A driver has been shot in the leg and has had his arm slashed with a knife during an attempted robbery in Sydney's west.

Police say the 24-year-old was sitting in his car on Hawksview Street, Merrylands, about 7.40pm on Saturday when three men walked up.

One man armed with a knife jumped into his passenger seat and demanded his phone and wallet. The driver fought off the intruder but his arm was cut and he was shot in the leg during the struggle.

He drove away and flagged down a passing motorist, who took him to hospital where he remains in a stable condition.

Police said they believe the attack was targeted.