Johnson is only one of two players to have featured in all 14 of the club's Championship games this season following promotion from League One last term.
However, the 23-year-old is out of contract next summer and would be able to follow in the footsteps of fans' favourite Jermaine Beckford by leaving on a free transfer.
A number of rival clubs are believed to be monitoring Johnson's contractual situation closely and preparing to make a move should Leeds fail to tie-up his services.