To correct the post above the quick answer is no.
The longer answer is if you have an unused leader, then you cannot get an MGL from elite attacks but you can still get additional SGLs from research projects. when they introduced the idea of getting leaders from research. I guess they forgot (or maybe just decided not to) install the same check for an existing leader that is made after an elite unit victory.
Edit: @Skibatized: For the record, the odds of an elite win producing an MGL are 1/16 from attacking and 1/32 from defending. If you have built the Heroic epic, these odds are reduced to 1/12 and 1/24 respectively. (Also are you getting confused with the limit on how many MGLs you can get and the number of armies you can have? You can never have more than one MGL in the game at any one time. You need four cities to support each army though.)