"When I heard that [Button] wouldn't do the Bahrain test, I wondered if he was taking it seriously enough," Australian Webber is quoted as saying by Speed Week.
"For me, if he's doing a triathlon in America rather than a test in Bahrain, I think first practice in Monaco will be a wake-up call for him. I just get the impression that he doesn't really care about it."
The former Red Bull driver said that Button's return is little more than a sideshow anyway, amid McLaren-Honda's crisis and the title fight between Ferrari and Mercedes.
"It's a non-story," he said.
"He'll drive, have problems with the fuel system, qualify 16th, retire after 12 laps or whatever. What's the point? Jenson is a world champion. He has won at Monaco.
"It would be a story if he could fight for the win, but to get a point if he's lucky, that really doesn't interest anyone."
The Monaco Grand Prix will take place on May 28.