“I Won’t Mind” features soulful vocals by Malik over a simple acoustic guitar loop and lyrics such as: “We are who we are when no one’s watching/And right from the start, you know I got you.”
One Direction, who have sold over 50 million records worldwide, announced last week that Malik was leaving the band but that they would continue as a foursome.
He said he was quitting because he wanted “to be a normal 22-year-old who is able to relax and have some private time”.
The new song was posted on Twitter by British producer Naughty Boy, who has previously worked with musicians including Emeli Sande.
But the move drew an angry reaction from One Direction’s Louis Tomlinson, who tweeted at Naughty Boy: “Wow @NaughtyBoyMusic you’re so inconsiderate pal, seriously how old are you ? Grow up! #masterofallwisdom”.
Tomlinson’s words were retweeted 320,000 times. Shortly after, he added: “Always have struggled to bite my tongue”.
Meanwhile, Naughty Boy faced a volley of abuse from One Direction fans for posting the demo but wrote that he would “let the music do the talking”.