Broja has always been a player of potential over substance.
He had a decent loan spell at Saints (3 years ago?) outside of that he's been either on the fringe of the Chelsea squad, disappointing in loan spells or injured, often a combination of any of those two factors.
It's now at the point that the talented young 20yo prospect is gonna be 24yo a few weeks into next season. At a certain point you have to look past the obvious potential with the talent he appears to have the possibility of and look at the reality.
To take any chance on him now, and for it to be worth it the following factors all have to occur.
He has to live up to his potential at the age of 24 having not improved over the 20yo version.
He has to stay fit, which in four years he's not managed ever to do.
He has to not only stay fit, improve on what he does decent already, but also add goals to his game - which as a striker is kind of his job.
I'd have misgivings about him on a free at this point, never mind throwing actual money to buy him - plus Chelsea will still do show think they can get a good fee for him.
Broja won't ever make it as a starter in this league as simply putting it, he can't stay fit and when he is fit he's not good enough to outweigh the long periods out.