If you go to Line-up, on the lower-right side of the map, you find an arrow. There you can change everything and about auto-subs it says they are automatical.
I don't to which point they are automatical. If an MR is injured and there's only an MC as sub, will he take his place, so making the formation irregular? Or will he go MC even if I already have 3 MC?
How does it work?