There is no player fatigue online at all.
Ive done scrimmage games with my friend and ran curtis martin 12 straight times in 1 drive with no impact and no auto subing happened either!
Same thing on defense stayed in goaline D 14 straight plays and not 1 player subed out...............WTF
raise your subin/out levels
My backs get tired and come out after about 3-5 straight plays, depending on the yardage