Injured Newcastle captain Andrew Johns was reportedly in hospital with a blood clot in his lungs after season-ending knee surgery.

The star halfback complained of chest pains and spent a sleepless night on Thursday struggling to breathe before seeing club specialist Dr Neil Halpin the Daily Telegraph reported.

He was admitted to Newcastle's John Hunter Hospital where scans confirmed the blood clot.

Johns was on medication to break down the clot and is expected to remain in hospital for up to three days.

"I was struggling to breathe and hardly slept at all last night," Johns told the Daily Telegraph.

Halpin said the clot was a serious health concern.

"People die from blood clotting," Halpin said.

"If it is not treated, it can be life-threatening."

Johns said he had been worried about the clot.

"I didn't know what was going on, I had to sit up to get my breath and I had these chest pains as well.

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