Jenson Button's future in Formula One will be determined by the performance of his McLaren this season, Mark Webber has predicted.
Button, 36, will begin the 17th season of his world championship career when the lights go out in Melbourne on Sunday.
The British former world champion looked poised to retire at the end of last year's miserable campaign - in which he scored just 16 points - before performing a dramatic U-turn to commit to the final term of his two-season deal with McLaren.
While the British team have shown improvement, in terms of reliability, during this winter's testing programme, their Honda engine still appears short on power in comparison to that of their rivals.
"He can do another season but there is a big call from McLaren and Honda as to what they can produce this year in terms of reliability," said Webber.
"There is nothing worse than having non-finishes. It is horrible for a driver to go through that effort, and you don't even see the chequered flag.
"So, they have got to get that reliability going, and that will be important for the drivers and to keep both their boys in the future.
"If they are operationally poor, in terms of reliability, it is a pain in the a*** at that point in your career. It's horrible."
Australian Webber started his grand prix career, which yielded nine wins from more than 200 starts, two years later than Button before announcing his retirement in 2013.
Webber, who was in contention for the 2010 championship before losing out to his then Red Bull team-mate Sebastian Vettel at the season decider in Abu Dhabi, faced numerous calls to hang up his crash helmet.
"JB has had a phenomenal career and there is nothing worse than being asked as a driver and an athlete, when are you going to retire," added Webber, who will work as a pundit for Channel 4 this season.
"If you are getting absolutely hosed, then it is a fair question. But the guy has got the passion to drive and he is still not that old, it is just he started young.
"Mentally, I think he has gone through a lot off the track in the last 12-18 months. He knows how Formula One works, but the next bit he doesn't know yet."
Button will partner Fernando Alonso at McLaren for a second year after the Spaniard resisted taking a sabbatical from the sport.
Webber, a close friend of two-time champion Alonso, said: "He just wants to be at the front maximising his potential.
"Last year, when he was fighting with some of the guys he was fighting with, Fernando has got more talent in his little finger.
"If you are knocking around with those guys, week in week out, it wears you down. That is a question for him and his drive and tenacity and determination.
"It is about that middle step on the podium for him. Would he love to parachute himself into a Mercedes? Of course he would."
:: Channel 4 is the new home of free-to-air Formula 1Â® in the UK with live coverage of 10 Grands Prix this season and comprehensive highlights of every race weekend. Visit www.channel4.com/F1 for more information.