Potentially It Could Cost You $10k To Repair Easily
If there is indeed a health-hazard mold in the house you better fix it immediately in order to limit further liability.
If your tenant has consulted one of those lawyers that is specialized in representing tenants in mold cases you are exposed to much bigger trouble. They will demand compensation for personal injuries in 100s of thousands dollars. Do not worry, they will find all kind of legal stands for sueing you.
I hope you have adquent landlord insurance to cover the repair and potential liability in case you do receive a letter from one of those ***** lawyers.
I suggest you order a mold inspection right a way. It takes about one week to get test report. If the report is negative your tenant will have no excuse. If it turn out to be bad you have to do what you have to do - fixing the mold and dealing with your insurance company or lawyers.