Williams suffered a mishap at training on Friday morning and will be assessed in the coming days. The injury is not expected to keep him sidelined for the Magpies' round 16 clash against Gold Coast.
Williams has played the last seven matches since being handed a suspended sentence for an assault charge earlier this year, re-establishing himself as an important member of the Magpies' back six.
Kennedy, who comes into the 25-man squad, which will be trimmed to 22 on Friday afternoon, last played in round seven, against the Blues.
He has played twice this season, for a career total of 14 games, but has enjoyed a strong run of form in the VFL.
Western Bulldogs forward Jarrad Grant has also been withdrawn from his team's squad for Sunday.
Grant copped a nasty hit to his nose last Saturday against Port Adelaide and has failed to recover in time to face Melbourne. His place in the 25-man squad has been taken by Fletcher Roberts.
