The 'Pillowtalk' hitmaker - who was previously engaged to Perrie Edwards - has only been dating the 21-year-old model for less than a year, but he has already asked her to be his wife.
However, Gigi reportedly rejected the proposal because she felt it was ''too fast'', and she also doesn't want to rush into tying the knot after seeing her mother Yolanda Hadid go through divorce twice.
A source told America's Life & Style magazine: ''She's only 21 and doesn't feel ready to tie the knot, so she turned him down.
''She's seen her mom go through two messy divorces, so Gigi wants to make 100 per cent sure Zayn's the one before she makes a lifetime commitment.''
While she may not want to marry the 23-year-old pop star, Gigi recently spoke of how proud she is of her boyfriend's solo career.
She said: ''I think that he really deserves recognition for the music that he made this year. It's been amazing to kind of see him learn about himself and the music that makes him really happy to sing.''
And the blonde beauty also admitted she much prefers Zayn's solo material to the work he did with his former band One Direction.
She shared: ''I grew up in a household where my stepdad was a classical musical producer - Andrea Bocelli, Josh Groban - that was the music I was into. I think we can all name a One Direction song that we like. Or maybe not. I love Zayn Malik solo a lot more!''
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