Police in Oshkosh said 21-year-old Michael T. Philbin of Ripon was last heard from around 2 a.m. Sunday. He had been visiting friends in Oshkosh that evening. He was reported missing on Sunday evening.
A police spokesman did not immediately return a message left Monday seeking additional comment.
"The Packers organization is aware of the missing person report regarding Michael Philbin, son of offensive coordinator Joe Philbin," Packers general manager Ted Thompson said in a statement. "Our thoughts and prayers are with the Philbin family during this difficult time."
A Brown County judge sentenced Michael Philbin to six months in jail in 2009 after he was convicted of sexually assaulting two young girls and two counts of battery.
His disappearance comes as the Packers prepare to face the New York Giants in an NFC playoff game Sunday in Green Bay.
Joe Philbin has been with the Packers since 2003, and has been the team's offensive coordinator since 2007. He interviewed for the Miami Dolphins' vacant head coaching job last week.