A representative for the singer did not respond to a request for comment from Page Six.
Zayn addressed fans directly on social media following his hospitalisation.
He said online: “To my fans – thank you to all of you for your love and support now and always – been a long week and am still unexpectedly recovering.”
He added: “Heartbroken that I can’t see you all this week, I wouldn’t be in the place I am today without you guys and am so thankful for your understanding.”
Zayn also thanked hospital staff, including nurses and cardiologists, saying: “You are all legends. Big big love xx z.”
The nature of the performer’s condition remains unclear, as he has not disclosed further details about his hospital treatment.
The cancellation of the Jimmy Fallon television appearance follows a disrupted promotional schedule, which had also included a planned event at the Rough Trade Below store in New York City on Monday.
Zayn is expected to begin a tour in May at the AO Arena in Manchester, with dates scheduled through to November, concluding in Miami.
The singer has been promoting the album and tour through social media in recent weeks.
His most recent tour, the Stairway to the Sky shows, stretched from November 2024 to March 2025.
During that period, his former One Direction bandmate Liam Payne died at the age of 31.
Zayn temporarily paused the tour before returning to the stage, where he paid tribute to the singer.
Zayn has a daughter, Khai, 5, with model Gigi Hadid.