Zayn Malik Cancels 'Tonight Show' Appearance After Hospitalization

Zayn Malik is hitting pause on his big comeback because his health just took center stage.

Sources familiar with the situation confirm to TMZ ... the singer has canceled his planned appearance on "The Tonight Show Starring Jimmy Fallon" set for Tuesday to promote his new album "Konnakol" ... after a scary hospitalization.

Zayn himself broke the news Friday, posting a photo from a hospital bed and telling fans he was "unexpectedly recovering" after a "long week." He didn't reveal what landed him there, but made it clear it was serious enough to derail his schedule.

He wrote he was "heartbroken" to miss fans, thanking them for their support and shouting out the "incredible" hospital staff who’ve been treating him.

Our sources tell us Zayn is stepping back from multiple commitments in addition to Fallon, including fan meet-and-greets as he continues dealing with ongoing health issues. We're told the decision came down to doctor's orders, and he's now seeking further treatment from what's being described as the number one cardiologist in the world.

PEOPLE first reported the news of the cancelation and his new doctor.

The timing is tough ... Zayn just dropped "Konnakol" and was lining up a full promo run ahead of his first-ever solo headline arena tour, set to kick off in North America this June.