He will at some point of course. His plan is to go to the World's again though first, which take place in October of next year, so he's an amateur until at least then by the looks of it.
Given that Flintoff is a cricketer who had a boxing match for a reality TV show and Joshua is the Olympic champion, it would be nothing short of premeditated murder.
Is this a joke? If not then you must be new to boxing right? Why don't you ask George Groves when he is going to fight Amir Khan.