Nationals manager Dave Martinez said that Williams is set to be placed on the bereavement list Monday, Jesse Dougherty of The Washington Post reports.
The transaction isn't expected to be made official until a few hours before the Nationals' series opener with the Brewers, which begins at 7:05 p.m. ET. Williams most recently started in the Nationals' loss to the Mets on Sunday, when he worked four innings while surrendering five runs on seven hits and four walks. The right-hander will likely be ready to return from bereavement leave before his next turn through the rotation comes up this weekend in Cincinnati.