Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE took a shot at Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE's stamina the day before Clinton is set to return from a break from the campaign trail after a bout with pneumonia.

The GOP nominee has steered clear of any controversial comments about Clinton's health since she appeared to stumble as she was whisked away from a 9/11 memorial event earlier this week. ADVERTISEMENT But he tip-toed into the waters Wednesday night during a rally in Canton, Ohio, questioning whether his Democratic opponent could keep up with his rigorous campaign schedule.

"You think this is easy, in this beautiful room that's 122 degrees?" Trump told the large crowd, straying from prepared remarks. "Do you think Hillary would be able to stand here for an hour? I don't think so. I don't think so."

He returned to the topic toward the end of his speech with a more sportsmanlike remark, but the crowd wasn't having it. "She's lying in bed getting better, and we want her better, we want her back on the trail. Right?" he asked the crowd. The audience responded with jeers and boos, with some shouts of "no," which Trump ignored. While he has shied away from the topic over the past few days, Trump has previously chided Clinton's health from the stump and questioned whether she has the "mental or physical stamina" to run the country.

Democrats have hammered Trump for questioning her health, accusing him of fanning the types of conspiracy theories that have gained traction on conservative websites.

His comments come just hours after Clinton's campaign released additional health records, including results from a recent check-up, in response to the diagnosis. She's been sidelined from the campaign trail since Sunday, but is set to return on Thursday in Greensboro, N.C.

Clinton had taken a few weeks away from public events late last month as the campaign ramped up its fundraising schedule. She's had 15 days off of the trail since August, compared to seven for Trump, according to CNN data . During that stretch, she held 81 events, including rallies, stops and fundraisers, compared to 90 for Trump.

Trump has not released a detailed physical report, but he shared a summary Wednesday with television's Dr. Mehmet Oz during a taping of Oz's show set to air Thursday. Those in attendance have told media outlets that Oz appeared impressed with Trump's fitness but noted that he's slightly overweight and should lose about 15 pounds.

Clinton campaign manager Robby Mook slammed that appearance as a "charade" that is "completely unserious" in a statement to reporters with the Clinton document release.