Manager would be good on one of the following features due to the fact he concentrates on the issue:
Coach: +25% increased speed of training of all players
Game strategist: +0.25% increased team performance during match
Leader: morale decrease effects would have only 75% effect
Fysio: fitness decrease effects would have only 75% effect
Entertainer: +100% increased number of fans per match, no fan loss in case of lost match
Scout: +2% bidding value, e.g. he would bid 100 but his bid shown would be 102. player selling ould get 100. amount to overbid would be 107
Youth coordinator: youth players would be generated from youth center faster by 25%
Groundsman: by better stadium set up the income from all home matches is increased by 40%
Motivator: every match played teamspirit would grow additional 1%
Doctor: once per 5 days he could heal fully one of his injured player
Administrator: +6 players in team (34+4=40)
Only one effect could be chosen same time. The change of concentration could be done soonest after 1 season (63 days) after previous change.
I bet implementing this would bring more specialisation and fun to the game ...
Of course this need some balance in values / skills and is subject of change for more funny effects
