The 23-year-old singer was a former band mate of the 'Pillowtalk' hitmaker before his departure from the group in 2015, and has said he doesn't ''understand'' why Zayn is against the idea of the 'What Makes You Beautiful' hitmakers - who went on hiatus at the end of the same year - reuniting in the future.
He told The Sun newspaper: ''He doesn't really support the cause.
''If he feels hurt and scorned in some sort of way that I don't really understand that's down to him so there we go.
''It is very sad because One Direction was a wonderful, wonderful time in all of our lives. It was like uni but on steroids, it was mad. It was so much fun and I don't understand how you can come out of that experience and say the things that he says sometimes, it doesn't make any sense to me but there you go.''
Zayn - who is in a relationship with model Gigi Hadid - previously said he needed a lot of ''time away'' from the hectic lifestyle he was thrown into during his time with the band, which also included members Niall Horan, Harry Styles, and Louis Tomlinson.
He said: ''I'm enjoying what I'm doing at the minute. When I was in the band, there were times where I needed time away to go see my family and recollect my thoughts. But right now, I feel like I have the time to process things, and I'm doing things in my own space, so it's a good place to be in.
''I feel myself growing every day as a person, as we all do, just getting older and wiser hopefully.''
And the 'Still Got Time' singer has spoken about his battle with anxiety both in the band and as a solo artist, and said that writing his experiences into his eponymously titled book was a ''therapy process'' for him.
Zayn added: ''I feel like writing anything down is a little bit of a therapy process ... It's a way of alleviating your mind and getting it out there. For me, it was a little bit of that. I kind of enjoyed it.
''It was fun to reminisce on things and think about what was good and what was bad and make sense of it all. I didn't have time to do that in the band.''
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