They hope to return to Rotherham and play at a new stadium, but have been told they are welcome to stay at Don Valley for as long as is needed.
"We have done all we could to allow this club to stay at Millmoor but I am not going to wallow in this, we are going to make sure that we make our time at Don Valley as exciting as it can be and trust that our supporters will back us through this period as they always have," said Stewart.
"We will work doubly hard with Rotherham Borough Council, and other interested parties to ensure that the new Community Stadium becomes a reality as soon as possible.
"In the meantime we will now press ahead with plans for the coming season which have been held up by the discussions over Millmoor."
United are due to head to the Don Valley Stadium for a friendly with Rotherham on Tuesday July 22.