From the wiki:
"Auto-substitutions are there to help you when you are not able to watch your match. You have 5 available positions where you can place desired players:
GK (goalkeeper)
DEF (defensive line)
WNG (AML/AMR and DML/DMR)
MID (midfield line
including ML and MR positions)
ST (striker)"
Here's my team:
Attachment 19758
I rather wish the autosubs were setup differently.