The former One Direction star has collaborated on a track with the Scottish singer but both want to feature it on their new albums, and the Irish hunk is willing to go to battle to have it on his record.
Speaking to BANG Showbiz at the BMI London Awards this week, the 'Nice to Meet Ya' hitmaker said: ''We (me and Lewis Capaldi) just sat down and wrote a tune. I haven't really heard it since but I think it's quite good. Maybe one day we could get it out.
''We might have to scrap for it though.''
Lewis recently admitted he wants Niall to release the duet so his bank balance will get a boost.
He said: ''We did do a song together. I love it.
''It's very good. But I would say that because I want him to release it because I like the money.
''We were in London with the same guys I wrote 'Someone You Loved' with, because they also wrote one of the songs on Niall's first record and stuff with One Direction.''
The Glaswegian recently revealed his bank card was declined at Glastonbury festival.
The 23-year-old singer was left red-faced when his debit card was rejected whilst buying shots for his celebrity pals after he made his debut on the Other Stage at the Somerset festival in June.
He recalled: ''I''m really s*** at transferring money on to cards.
''I just played and I was so excited so I was like, 'Let's get some shots', and then I completed f***ed it.
''I think Jack Whitehall's sister's fiance paid as I f***ed it.''
The 'Hold Me While You Wait' hitmaker has become a breakout superstar since he released his hit single 'Someone You Loved' this year, but he still lives with his parents in Scotland because he doesn't earn as much as people think - while he splashes what he does have on grub.
He recently said: ''There's always room to earn more. I still live with my parents so I don't think I am earning that much money!
''And all I spend my money on is food because I can't help stuffing my face. I am splurging on food and it shows, it's showing on my gut, my gut is expanding every day.''
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