Correct me if I'm wrong, but I feel like you're thinking this might be more of a confrontation (why are we so far behind?!) than a conversation. The best thing is to state facts, "Hi Director. So, right now we have pages 1-4 and 12-15 blocked. Great! What's are you thinking for for next week? Maybe blah and blah as they tie into blah? Should we schedule the fight director for next week? If we block through 30, we'll cover that section," etc. Just calm, knowledgable and helpful.
Also, do you have a production manager/producer/department head who can prod him about scheduling? I've run into this quite a few times, where wires are crossed and no one knows who's supposed to talk to and schedule someone.