Japan's Kazuki Nakajima has potential as a future Formula One driver but Austrian Alex Wurz may not retain his drive next year, team boss Frank Williams said on Friday.
"Alex has been very reliable but I am not sure whether he is going to race again next year," Williams told a news conference at the Chinese Grand Prix.
"Nakajima - too soon to say if he will have an outstanding future or a medium future in F1, but I think he is Formula One material."
Nakajima, 22-year-old son of former F1 racer Satoru Nakajima and a member of Toyota's young driver programme, joined Toyota-powered Williams last November as a test driver.
Wurz, 33, was a test driver with the team before being promoted to the race drive this year after Australian Mark Webber's departure for Red Bull. The Austrian has scored 13 points to teammate Nico Rosberg's 15.
"I think Nico is a star of the future," Williams said of his German driver, son of Finland's 1982 world champion Keke.