The younger Schumacher said no deal had been struck and his manager said he would consider other options if the negotiations failed.
The German driver, who attended a gala of Williams's partners BMW on Saturday in Seefeld, Austria, reluctantly confirmed media reports that the discussions with Williams were difficult.
"These are internal matters over which I can't talk," he said. "I am not totally satisfied and that's why it's still going on.
"It is not about money but there are things that still have to be cleared."
Willi Weber, the manager of world champion Michael and Ralf Schumacher, said one of the problems was the number of personal sponsors Ralf would be allowed to have if he kept driving for Williams.
"We are talking about five contracts between us and Williams and they each have 100 pages," he said.
"We're not under any kind of pressure. Ralf belongs to the top drivers and there would be other options. If the conditions (at Williams) are not right, we will not sign."
