Bosh started feeling ill over All-Star Weekend in New York, complaining of discomfort in his rib area. He played in the All-Star Game on Sunday, scoring 10 points in 11 minutes.
Initial tests were on Bosh's lungs, sources told the Miami Herald and The Associated Press. Bosh and the team were expecting to have a better grasp of the situation Friday, the AP reported, citing a source with knowledge of the situation.
Bosh spent the early part of this week on vacation with family and friends, including teammate Dwyane Wade, in Haiti.
When he wasn't feeling better by Wednesday, he was sent by the team from practice to a team doctor. He was later sent to a hospital for tests and then admitted.
"I don't know if he was sick (in Haiti). I'm not a doctor," Wade told reporters Thursday. "I just know he wasn't feeling good. He wasn't coughing or throwing up, but he just wasn't feeling good. So I don't know when it happened. It could have happened in New York."
Heat coach Erik Spoelstra said at Thursday afternoon's practice that Bosh was "under the weather" but offered no specifics.
Miami plays at New York on Friday night. Bosh did not fly with the team Thursday.
Bosh is averaging 21.1 points and 7.0 rebounds this season.
Information from The Associated Press was used in this report.