The source went on to add, "They have insane work schedules that would put pressure on any relationship".
Following the news of their break up, Malik posted a cryptic-sounding message on Instagram.
According to The Sun, Zayn, 25, and Gigi, 22, - who were recently rumoured to be engaged - made the decision to split after their busy schedules added strain and distance to their high-profile romance.
Hadid also took to Twitter to confirm the split, and said she will be "forever grateful" for the time she spent with the "Pillowtalk" singer.
'When Life throws you lemons, catch em so they don't hit you in the fucking face, ' he captioned a brooding selfie on Instagram earlier on today - hours before the report of the split broke.
Hadid, 22, and Malik, 25, met at a Victoria's Secret Fashion Show after party in November 2015, and had briefly broken up in June 2016. He spoke to ES magazine and said, "She's a very intelligent woman". "She's not like, arrogant in any way, she's confident".
This isn't the first time the couple has broken up over the course of the past couple of years, either. Just two months ago, Hadid posted a sweet photo of Malik on her Instagram, to celebrate his birthday. She wished him a happy 25th birthday and confessed that how much she loves him.
Adding that she embraced him like a son, Dutch beauty Yolanada said: 'He's a handsome human being from Bradford, England.