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LeBron James’ mysterious chest injury is continuing to cause pain, and now some more serious concern.

On the advice of Cavaliers team physicians, James was admitted to the Cleveland Clinic late Wednesday for tests on his left strained pectoral muscle.

He underwent a battery of tests and was kept overnight because he had a fever. He is expected to be released Friday.

James took part in the Cavs’ light practice Wednesday after skipping Tuesday’s game in Pittsburgh with the chest pain. As the day went on, the discomfort worsened. Concerned about the region of the pain, James was encouraged to get himself checked out.

General manager Danny Ferry, who along with coach Mike Brown joined James at the hospital, said all tests have been negative and there is no evidence at this point to suggest it is anything but the original diagnosis of a strained muscle.

“It was just as a precaution, we went in and wanted to have tests to make sure he checks out well,” Ferry said. “All the test results we have back so far have been good and there is nothing to be concerned about.”

The first concern was that it would be some sort of muscle tear instead of a strain. Additionally any time there is chest pain for any reason, it can be scary. Ferry said to his understanding it is just a muscle injury and tests have been run to make sure it isn’t anything else. He said he was optimistic the injury was not serious.

James isn’t sure when he suffered the injury, saying he felt the pain when he woke up Tuesday morning in Pittsburgh. Chances are he suffered the strain during Monday’s exhibition opener in Washington against the Wizards.

Team officials said James’ spirits were good and they hoped he would rejoin the team Thursday, though it is doubtful he’d play against the Philadelphia 76ers or in Saturday’s game in Milwaukee. Doctors have ordered him to rest.

“Everybody is human, everybody has their ups and downs,” Brown said. “We’ve run a lot of tests and everything has come out fine. If he has discomfort the best thing to do is error on the side of caution.”