The loss of training between 48+ and 48 is probably small, but then again, so is the coach impact.
What I'm saying, I'm training some lower potential players, so I never minded about loss of minutes, injuries, and I always used cheap lvl 3 coaches.
Now, if I was training that franchise player, NT star, MVP+, I would go after a no less than level 7 coach, and I would worry about every missed second. 48? Play him as a backup in another game :) Injury? Go crazy for days :)