SSI is for people with less than $2000 in assets, so, yes, you will be ineligible for SSI.
Be sure to designate "best answer." If you live in Oregon, you may call me for more detailed advice, 503-650-9662. Please be aware that each answer on this website is based upon the facts, or lack thereof, provided in the question. To be sure you get complete and comprehensive answers, based upon the totality of your situation, contact a local attorney who specializes in the area of law that involves your legal problem. Diane L. Gruber has been practicing law in Oregon for 26 years, specializing in family law, bankruptcy, estate planning and probate. Note: Diane L. Gruber does not represent you until a written fee agreement has been signed by you and Diane L. Gruber, and the fee listed in the agreement has been paid.
Holding on to the check, sending it back or refusing to cash it could also be considered enough to cause you to lose your benefits. You may however be able to put the check in a special needs or pooled trust and still retain your benefits. The funds in the trust get spent on you, but are not available for Medicaid/SSI purposes. A 1st party or d4A special needs trust is going to cost you money to set it up. They are complicated and can take time getting it approved by the State and SSA. You may have to go to court as it can only be established by a parent, grandparent, guardian or the court. A pooled trust on the other hand will have already been written and all you need to do is open an account and assign the check to the trust. This is something you can do on your own. You should contact an elder law attorney in your area. They should be able to explain the process to you and help you out. You can locate one doing an AVVO Find a Lawyer search or by going to the National Academy of Elder Law Attorneys website at www.naela.org.
I edited the practice area to "Social Security," which should hopefully help some attorneys who work with Social Security Disability to see your question.
I think it would be a good idea for you to speak with an attorney who handles SSI. They will be able to tell you how this will affect your benefits.