The previous owner of our home allowed water to work it's way into plywood subfloor in bathroom, underneath vinyl flooring. A section about 2 feet by 8 inches of the subfloor is rotten about a quarter of the way through the subfloor.

Do I need to remove the entire subfloor or can I just cut out the rotten section? How do I go about removing the rotten section? Is there a product that can patch wooden subfloors? I plan on eventually installing ceramic tile in this space, including cement board.

Thanks for any suggestions or help you can provide!