Yes possibly an easy fix, take it in.

What crank do you have? It's likely as simple as tightening it up with an allen key in about 30 seconds.

Rotor 3d+ on a Cervelo P2 (the fsa was taken off a year ago when the power2max was put on).

Did get the chainrings swapped over to osymetrics around 6 weeks ago.

I assume that the chainrings are tight.

If the crank is loose, there are two things to do.

Drive-side: 8mm allen wrench.
Non-Drive-Side: There is a ring just inside of the crank arm. Loosen the tiny bolt on a ring with a 2mm allen key. The ring can be rotated to remove any play from the crank.

That doesn't look good... I assume the black chunk surrounding the small screw should be attached to the rest of the black ring.

Thanks for the help, looking at some YouTube this would seem to be the solution.

Tighening up the lock ring should take the play out of it, only problem is that the (broken) lock ring won’t move even with the screw backed out.

From what I can infer it looks like the cranks won’t fall off, but getting the wobble out short term appears to be a washer-Job or some brutality towards that lock ring & a replacement.

Double bother.

If you don't already have some BB30 spacers/shims on hand pick some up from your LBS that carries them. Get a 0.5mm, a 0.7mm and a 1mm just in case (what I recommend). A 0.5mm alone might not be enough to remove all the play because of compression so it's good to have alternate sizes on hand too.

I believe 0.5mm is the smallest you can get but if a smaller one exists get one of those too just in case.

Shoot. Not good, but not end of world.

That preload adjustment ring is what is responsible for taking out that last bit of play in your cranks. That screw locks the ring in place once snug.

You should still be able to snug up the crank with the ring, but it will keep working itself loose. I have no idea how long that would take.

This is what you need to replace

Thanks for the pointer.

Am I right in thinking this is rideable? Could a local bike store throw a quick spacer in there to get the play out before getting the replacement?

It's not likely a safety issue, but may be an annoyance if it's out of alignment when shifting.

yes, a shop could throw a spacer ring, or ring washer on to take out the play in the crank.

Head to the local cervelo dealer. They should have a bunch of bikes on the wall with rotor cranks or will probably have a bin full of spares.

If that doesn't work out, all you need is to take up the play in the crank. Spacers and a wave washer or a sram preload adjuster may do the trick.

Excellent, thanks for the help, very much appreciated