Erwin has impressed at Boundary Park this season, establishing himself as a mainstay of the team that finished 17th in the league and scoring 10 goals in 40 matches in all competitions.
He is yet to make an impact for Leeds following his arrival from Motherwell in 2015, with his 12 senior appearances yet to yield a single goal.
Leeds are likely to overhaul their forward ranks this summer irrespective of whether they are able to hang on to Championship leading scorer Chris Wood.
Manager Garry Monk made it clear he wanted a new striker in the January transfer window but the club ended up signing two wingers on loan instead.
In the latest Leeds United transfer news, rivals have stepped aside to give the Yorkshire giants a clear path to the summer signing of a £3million player of the year striker.