"...every goal against..." in the league that totals 15 from the 21 games.
Shouldn't take him too long at all to see what the problem or who is at fault for each goal against this season. A couple of hours max?!
The league's clear best defensive record and it's not a fluke.
I'd politely suggest the manager and coaches if not already doing so should instead be re-watching the match tapes to examine the reasons why we aren't creating lots of chances at the other end of the pitch.