Former Formula One driver Johnny Herbert says Jenson Button needs to 'pull his socks up'.
Herbert, who won the British Grand Prix in 1995, also says accusations that Eddie Irvine is too old to race at 36 are untrue.
His comments come after Button slammed Irvine in the national press, claiming the Irishman was past it.
Herbert said: "Jenson's a young wipper snapper!
"As long as you've got the desire to race, then age is not a problem. Damon (Hill) and (Nigel) Mansell both managed it, so age is not such a big thing."
Herbert is also sure Jaguar driver Irvine still has the desire to race, even though his two seasons with the Milton Keynes-based team have not been his most successful.
He said: "I'm sure the desire is still there when he gets in the car. He just needs to perform to the best of his ability."
Herbert offered the same advice to Button, who was regularly out-qualified by team mate Giancarlo Fisichella last season, saying: "Jenson needs to pull his socks up.
"He had a poor year last year, and he has got to do better this year."