The Bradford-born singer, 29, launched a solo career after leaving One Direction in 2015, a year before the boy band went on an indefinite hiatus.
On Tuesday, Malik posted a black and white video on Instagram singing an a cappella version of Night Changes from the band’s fourth album, sending fans into a frenzy.
Shocked fans sent messages of support with the move prompting others to ask what he was trying to tell them.
“OMG what could this mean? Something is happening,” declared one excited user in the comments section.
“Come on comeback! COME ON REUNION TOUR,” pleaded a second, with another agreeing: “1D reunion = what we all want.”
Others were quick to point out it is the second time this year he has sung a One Direction tune, having posted an Instagram video on June 11 singing You And I from their 2013 album Midnight Memories.
“Does he just randomly pick 1D songs to post or do you think he’s missing 1D right now? He now has sung You & I and Night Changes,” pondered one.
“This is the second time. It can’t be a coincidence,” assessed another.
His former One Direction bandmates Harry Styles, Louis Tomlinson, Niall Horan and Liam Payne have yet to comment on the video.
He may be waiting a while for feedback from Payne, who recently said in an interview with controversial YouTube star Logan Paul that there are “many reasons why I dislike him”.
In October, Malik pleaded no contest to claims of harassment after allegedly launching a tirade against ex Gigi Hadid’s mother, 57-year-old Dutch-American socialite Yolanda Hadid.
He was placed on 90 days probation on all four counts for a total of 360 days, and was told to complete an anger management class and a domestic violence programme.
Malik and model Gigi, 27, share one-year-old daughter Khai.
The singer, whose most recent album Nobody Is Listening peaked at 17 in the UK albums chart, previously dated Little Mix star Perrie Edwards.