This is unlocked along the way to:
And the solution on that involving Burn Returners is the best method to get this done.
After every game you finish, go to your roster and buy a bunch of experience on the Burn Returner. Upgrade their key stats first, then move on to whatever else to work your way toward All-Star.
This may not unlock til you start another game or two (make sure you are in control of your team)