Whittaker impressed this season while on loan at League One club Plymouth Argyle, helping the team sit top of the table.
The forward has now been called back from his loan spell though and Rangers are interested in taking him on.
Rangers lodged a bid with Swansea for the forward, which was turned down by the Swans, but the Gers are insistent.
Negotiations are still going on in the background to bring Whittaker to Ibrox as Rangers have not given up his pursuit.
The 22-year old is thought to be keen himself on a move to Rangers and Gers boss Michael Beale has also publicly acknowledged the forward.
Whittaker played 25 League One games for Plymouth and scored nine times in addition to assisting seven goals before being recalled back to Swansea, where he has not played a single match since.
Aside from Whittaker, Rangers are also interested in his fellow Championship star, Norwich City midfielder Todd Cantwell.
