Can you give him extra pellets? Its not ideal but will be OK temporarily, important thing is to keep him eating regularly so he doesn’t go into stasis.

These are suggestions commonly given for temporary no-hay situations: “Running out of hay is not optimal, but if you at least have pellets, you can increase and split their daily portion over the course of the day into at least 3 feedings to make sure that they are still eating throughout the day. If you have a yard with grass, you can also harvest fresh grass to feed your rabbit until you can obtain more hay. If you still have access to fresh greens, we would recommend increasing that portion as well. Try to offer more chew toys such as rabbit-safe branches and grass mats to help with teeth wear in the meantime. However, do watch out for signs of poopy butt as some rabbits may get messy behinds from the lack of fiber in the diet. We would recommend stocking up on recovery foods such as Critical Care and grass hay cubes or hay stacks as a double backup if you do not have space to store much hay.” – Rabbitors Discord