"It's complete rubbish," the German, winner of nine grands prix so far this season, said as he and Hamilton joined factory-based employees on Tuesday to celebrate the team's third successive constructors' championship.
"He's on it as ever before, fully motivated and does massive work hours also. I've seldom seen that from him in the last years, such a large amount," he told Sky Sports television at the team's Brackley headquarters.
British media, whose criticism of Hamilton's use of Snapchat during a news conference in Suzuka led to a backlash from the driver who also walked out of another media session, had questioned his state of mind.
Monday's papers talked of a 'delicate ego', examined his 'fragile mental state' and suggested the Briton was losing it on and off the track.
"Executives were mouthing the word 'meltdown'," reported the Times newspaper, which said the champion had gone from "cocky prankster to sullen loser".
Mercedes motorsport head Toto Wolff said it was clear the media needed to produce headlines, building up and knocking down.
"Lewis had a couple of tough weekends... if he recovers and has a good weekend in Austin, he's the hero again," he said. "That's why I'm pretty relaxed about it."
The two drivers earlier visited the Mercedes high performance engines facility at Brixworth, where they also joined staff for a team photograph, signed autographs and posed for selfies.
