The track, which began its chart ascent seven weeks ago, will mark the singer's fifth UK number one song if it retains its lead until Sunday's official announcement.
The Bajan star's previous number ones are 'Umbrella', 'Take A Bow', 'Run This Town' with Jay-Z and Kanye West, and her last effort, 'Only Girl (In The World)'.
Elsewhere on the chart, drum 'n' bass duo Nero currently stand at 16 with 'Me And You', while Cee Lo Green's 'It's OK' enters at 26.
Martin Solveig and Dragonette's 'Hello' is on course to land at number 37, marking the French DJ's first UK Top 40 hit in five years, and Professor Green's 'Jungle' featuring Maverick debuts at 40.
On the album chart, Plan B's The Defamation Of Strickland Banks looks set to return the top spot eight months since it first peaked at number one.
Cee Lo Green's The Ladykiller is set to achieve its highest chart position to date, leaping nine places this week to number four, and Rumer's Seasons Of My Soul is on course to return to the top ten, vaulting from 21 to number six.
The official chart is announced on Sundays between 4pm and 7pm.
Source: Official Charts Company.