"I saw what was going on with her and I said, 'You know, I'm going to go do something and I actually took a physical last week and probably, I guess this week, will release the results of it," the Republican presidential nominee told "Squawk Box" in a telephone interview.
Trump made his remarks a day after his 68-year-old rival left Sunday's 9/11 memorial at ground zero after she felt "overheated," according to her campaign. She had to be helped into van. A note from her doctor released later Sunday said she had been diagnosed with pneumonia on Friday.
Clinton was taken to daughter Chelsea's New York apartment. About two hours later, she emerged and told onlookers: "It's a beautiful day in New York." She said she was "feeling better," according to NBC News.
"It's quite sad," Trump said. "I hope she gets well soon."
"It's interesting because they say pneumonia, but she was coughing very, very badly a week ago," the 70-year-old Trump said. "It's very interesting to see what's going on."
Clinton canceled a campaign fundraising trip to California scheduled for Monday and Tuesday in order to rest.
"It is a very tough schedule. You go from one city, you go to Pennsylvania, Ohio, and Florida, you know, all over," Trump said. "It's grueling work. There's no question about it."
In August, Trump's doctor said he wrote a letter declaring Trump would be the healthiest president in history in just five minutes while a limo sent by the candidate waited outside his Manhattan office, NBC News reported.