"Plus you know our luck with injuries!"
Mainly due to the previous manager who's history is renowned for driving players into the ground, see the Scottish Record where even he admitted that when he was at Celtic.
His long term injury was not through training, some injuries happen in training, it wasn't a tackle he made. I thought that would be pretty clear.
Every team has a DM, that usually play with a couple of AM's. It is a specified position in a game of football.
Gallagher played 33 games last season for Madrid, 3 goals 3 assists as a DM
Baena an AM scored 7, 9 assists in 32 games.
One player a DM and the other an AM two completely different players.
"Just defending or attacking in midfield is outdated"
I think you are way off the mark on that assumption.