Jenson Button said he is in "good talks" with McLaren about his future but declined to say if he will retire at the end of the season.
The 35-year-old, who McLaren have a contractual option on for 2016, said he had "many possibilities" for next year but could not give "more information".
If he quits or McLaren drop him, one of their reserve drivers, Kevin Magnussen or Stoffel Vandoorne, would step in.
Two-time champion Fernando Alonso is contracted to McLaren until 2017.
Speaking before this weekend's Japanese Grand Prix, Button said he was not enjoying struggling towards the back of the field, as McLaren have been this year following their switch to Honda engines.
"I don't think any driver has joy when they're not fighting for victories," said the 2009 world champion.
"That's what we're here to do. It's the challenge of fighting at the front.
"I don't like being 10th. Or 14th. But there is the possibility of joy coming back and that is a challenge. After the Singapore Grand Prix I wasn't joyful."
Button retired from Sunday's race in Singapore after spending much of it battling towards the rear of the field, but said on Thursday that he expected McLaren to be winning races in future.
"This team will achieve in the future; I don't know when," he added.
"A lot is missing but the important thing is to understand what is missing and we do understand. It could happen very quickly or it could take a few more years. I don't know the answer to that."
Button stressed that he would not join another F1 team, but McLaren would have to be more competitive in future.
"If I am in F1, I will 100% be with McLaren-Honda. If I was in F1, I would definitely want to be with this team," said Button.
"If I think there is going to be a positive future, of course I would love to compete. I am a racing driver, I want to go and win."
Asked if would consider racing in the Le Mans 24-hour sportscar race next year, he said: "I've never thought about doing both.
"With a 22-race F1 calendar, you're going to be very limited on weekends. And sometimes it's nice to have a weekend off.
"I cannot see that happening. With that many races you're not going to be doing much else. I don't think it will really work for me."
Ferrari's Sebastian Vettel said Button would be missed if he decided not to continue next season.
"It would be a big loss," the four-time champion said. "He is a big character.
"We know he is quick. He deserves to be a champion. I'm sure if there were more years when he had the package to win he would have had a big say in it.
"The quality is without doubt and he is a fair guy on the track. We all like him for many reasons."
|Japanese Grand Prix|
|Venue: Suzuka, Japan. Dates: 25-27 September.|
|Coverage: First and second practices - Friday, 25 September - 01:55 BST and 05:55 BST on BBC Two and BBC Radio 5 live sports extra. Final practice - Saturday, 26 September - 03:55 BST on BBC Two and BBC Radio 5 live sports extra.|
|Qualifying - Saturday, 26 September - 06:00 BST on BBC One and 06:55 BST BBC Radio 5 live sports extra.|
|Race - Sunday, 27 September - from 05:00 BST on BBC One and from 05:30 BST on BBC Radio 5 live|
|Full live text commentaries will also be available on the BBC Sport website, mobile and app.|