Mark Webber believes Jenson Button is "not very interested" in his one-off return to Formula 1, standing in for McLaren's Fernando Alonso at the Monaco Grand Prix.
Alonso will skip the Monaco race later this month to make his debut in the Indianapolis 500 in a McLaren-Honda-Andretti entry, with Button called up as part of his role as the team's third driver.
Button has not driven a 2017-specification F1 car, not taking part in the post-Bahrain GP test after his drive was locked in, meaning his first laps in McLaren's MCL32 will come in practice at Monaco.
Webber, who raced alongside Button in F1 between 2002 and '13, takes that as evidence the 2009 world champion isn't fully committed.
"It's a non-story, Jenson at Monaco," said Webber.
"He goes out, has fuel pressure problems in FP1, qualifies 17th, retires on lap 12 of the race. Whatever, who cares?
"Jenson didn't do any testing in Bahrain, he doesn't take it so seriously - 'I want to stay in America and do my triathlon, I'm not bothered about the Bahrain test' - which for me was a surprise.
"The first session in Monaco will be wakey-wakey. I don't think he's very interested.
"I don't think he would have been first on the phone [about replacing Alonso]."
ALONSO RUNNING McLAREN
McLaren-Honda has struggled so far in 2017, with Monaco considered the team's best chance for a competitive showing.
Webber believes that Alonso's absence for the weekend will help his rookie team-mate Stoffel Vandoorne.
"I like Stoffel a lot, he's got his head screwed on," said Webber.
"He sees the big picture quite nicely for his age, he has a very good career in front of him.
"This is a good learning [process] for him in this car, with Fernando in the other garage. Fernando is running the team at the moment, he's running McLaren.
"Fernando is colossal, mercurial. So for Stoffel, it's good learning."