How many pros CAN'T manual?

Probably none. I think it's a requirement to be a pro!

I'm not embarrassed to admit that I cannot manual, either. I can barely wheelie.

I am embarrassed to admit the same.
It's one of those goals that rears its head every few months...

It kinda depends on your definition of 'manual' as far as if pro riders can or can't. to be riding along on flat ground and manual at will, for 100 feet or so, I'd guess half of the pro (gravity) field could do that. A couple rolls on a trail? That's getting close to 100%. For the women, I'm married to one pro that can't manual on call, but has done it in a roller setting.

colin bailey seems to think there are plenty who can't.

Colin going off about having try outs in order to be on the team was pretty amusing.

Vital needs to run the 2020 #mountainbikecombine

We can test the up and comers/privateers on things like...

Manual distance
Bunnyhop height
Front wheel skid lenght
Long Jump
Huck to flat height
Riding backwards
Two wheel drift speed
Wheeling through an obstacle course

...and so much more

Depends on the discipline really, my guess is that many XC pros can't manual over a few meters, some top enduro riders have mentioned things along those lines (FBM said he can't manual, Jerome Clementz said he wanted to learn how to whip). For those Disciplines, I get how that isn't something that naturally helps their performance or is part of training.

I believe most DH riders ride BMX/pump track as part of cross training, so I imagine for manualing skills it is closer to 100%.

I can't manual and it kills my self-esteem.

+1! I can wheelie all day long but no manual.

Manual is coasting with no pedaling, a wheelie is when pedaling.

I'd argue that a true manual is coasting wheelie off the seat; standing only.

For the question I can manual on demand for up to 15 ft or 5m, after that my consistency falls way off. Sometimes I can get a good one going most times not. For reference I can wheelie all day long, am able to make turns, wheelie fast or slow and am able to coast the wheelie for length too.

I find manualing much harder than wheelieing.

I think that to be functional for trail needs, racing etc you only need to be able to manual for 2-5 meters. That will get you through most any dip, water crossing, etc where manualing helps.

I dream of being able to hold kilometer long manuals!

I can manual and wheelie for days, but sit down, feet off manuals have always eluded me.