Newport striker Shawn McCoulsky has been diagnosed with pericarditis.
McCoulsky, on loan from Bristol City, is undergoing tests for the heart condition after suffering from chest pains that led to a hospital visit.
The 21-year-old is Newport's top scorer this term with 11 goals, and scored the winner when they knocked Leeds United out of the FA Cup in January.
"He's had chest pains and he's been checked out by the hospital," manager Michael Flynn explained.
"It's something called pericarditis
"The doctor spoke to Bristol City yesterday and I'd obviously never risk a players' health."
Pericarditis is inflammation of the fibrous sac surrounding the heart, known as the pericardium.
McCoulsky last played for the Exiles on 24 March and will miss the home clash with Stevenage on Saturday.