The 25-year-old, currently on loan at Tondela from fellow Portuguese side Maritimo, had to be rushed to hospital last week after falling ill.
Doctors found the footballer had a bilateral pulmonary thromboembolism, a condition that could have cost him his life.
He’s immediately been ruled out for the rest of the season and faces the possibility of his football career finishing prematurely. Balde will be monitored closely over the coming weeks before a decision is made.
Balde spent one season in the Celtic first-team after joining for a £1.5million fee from Vitória Guimarães. He scored only three times for the Scottish champions before being loaned out and ultimately released in 2015.