If you were training him hard pre game it might have had an effect on his performance
yes, good point. I still remember when I 've lost in a Cup semifinal in lv3.
I trained my players (most of the squad) 3 times, 3bars practice, gave them greens and then they performed unexpectedly bad in the afternoon game.
Also, if you have some gathered sp and give them only in one skill (attack for example) then it can change the balance of the player (some times for good, some times for bad).
but in general, no for me.