San Jose Police Department Sgt. Heather Randol said Wednesday that detectives searched McDonald's San Jose home.
Randol said an area hospital notified police Tuesday night that a woman was seeking treatment.
According to police, the woman told police she was "possibly" sexually assaulted by McDonald. No arrests have been made or charges filed.
McDonald could not be immediately reached for comment. San Francisco 49ers spokesman Dan Beckler didn't immediately return a phone call.
An NFL spokesperson said the league is looking into the matter when reached by NFL Media.
The Santa Clara County district attorney's office said Nov. 10 that it declined to file charges against the defensive lineman in a domestic violence investigation stemming from his Aug. 31 arrest. McDonald has played the entire season with the 49ers.
UPDATE:49ers general manager Trent Baalke announced later Monday that team has decided to release McDonald from his contract.
The Associated Press contributed to this report.