Mckay, 26, has been Inverness' top scorer for the past two seasons and has netted 10 times in the Scottish Premiership in 2014-15.
Mackay's Wigan side have been struggling for goals, scoring just 26 times in 27 Championship to sit second bottom.
Inverness chairman Kenny Cameron confirmed in a statement on the club's official website: "The board of Inverness Caledonian Thistle FC agreed to allow Billy Mckay leave to travel to DW Stadium for discussion of personal terms with a view to an immediate transfer.
"Billy has never hidden his ambition to compete at the highest possible level and has always conducted himself in a professional manner in this regard.
"We are forever mindful of the risk of losing players during any transfer window and, as always, have contingency plans in place should agreement on personal terms be reached with Billy."
