Last season we got 4th, at least in part because we were playing mainly once a week, and this meant that all the players were fresh (ideally they want 5 or more days rest between games - so playing once a week does this) and it also allows the manager to do a good deal of coaching and preparing players for particular opposition games
So going deep in both FA Cup or CL might prejudice the above as we'd play games every 3 or 4 days for a few weeks - do we have enough players to rotate the team enough to rest the players ? Might be tough on our 3 CM's in particular ?
Its not impossible ........ but imo would require manager to rotate some players to keep players fresh, and that's not been something management has been good at (except v Preston)