The fork on the foot shift just popped off the shift shaft...most likely. This can happen if you loosen the nut holding the foot shifter or push/pull on the lever. I have seen this occur a couple of times when a rig is loaded/unloaded from a truck or trailer and the shift lever gets bumped hard while muscling the rig in/out. Go to my site and look at the pics in the gear box chapter. If you can mentally visualize the parts, you can put the fork back on with a little patience...kind of like cracking a combination lock. Otherwise, you will need to remove the g.b. and split it slightly like you are putting back together (see my site again). Peer into the split and line the fork up and smack the case together again.
It is Russian after all, and there is a outside chance that something did break, maybe...but that would be rare