How does FIFA 13 choose which player you get in the challenges before the match starts? Is there anyway you can choose it yourself?
This answer is not entirely factual, and I guess it would be hard to confirm without having some insider knowledge anyway, but this is generally what I have noticed.
I am in my 5th career season as Yeovil Town FC (Go Glovers!) and have reached the premier league which allowed me enough cash to purchase Neymar.
The player that is selected for challenges will always be one from your starting 11, I have never seen a substitute (or excluded squad member) selected. If I have Neymar in my starting 11, it is always him selected - for me, this indicates that it is based on the player with the highest rating.
So then we have to wonder, is it highest overall rating? or highest stats for attributes related to the challenge? Again, it's hard to know for sure, but Neymar is not my FK specialist and has about 5-10 less stats in all the FK related attributes, yet neymar is always chosen even for the free kick challenges. Based on that I would say that it is the player with the highest overall rating that is selected.
My only doubt would be that it may be based on a shooting stat instead because the most common challenges in career mode warm-up are goal scoring ones, with the exception of the tennis style one, which I always get Neymar matched with my other forward/striker (I player 2 up front, Neymar and another).
Of course, Neymar also happens to be my top goalscorer for the seasons I have had him - this could also be a/the deciding factor.
Prior to acquiring Neymar, I distinctly remember my forwards always being the ones selected, and from what I remember it was always my best one at the time.
In short, I would say, it is always your best forward.