"He has to try to build arm strength. To take him into a pressure situation right now with him not having enough innings in spring -- it's not fair," Williams said.
Mattheus said his arm is in great shape and feels he could be ready for Opening Day.
"I feel great," he said. "I do need a workload, I do need a few more innings. But I came into camp in shape. The arm being in shape is not going to be a question."
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also could be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.