McCormack has been left out of Leeds' pre-season trip to Italy, as his future at the club remains in doubt.
Fulham have now returned with a second offer for the Scottish international, whilst other clubs also look to engage Leeds in talks.
However, no club has yet been able to agree a deal with Leeds owner Massimo Cellino and McCormack has now officially indicated to the club his desire to leave.
Having met with Cellino in the past week, McCormack has now handed in an official request as he looks to move on.
McCormack is one of the most in-demand players outside the Premier League having finished last season as top-scorer in the Championship.