Former Notre Dame defensive lineman Ian Williams was SI.com draft analyst Tony Pauline’s No. 1-rated undrafted prospect entering the rookie free agent signing period Monday night.

On Monday evening, Williams informed PFT that he will sign with the San Francisco 49ers.

A 6-foot-1, 319-pound nose tackle, Williams was not selected in April’s draft due to medical concerns. Williams missed four games with a knee injury as a senior, although he returned to play in the Sun Bowl against the Miami Hurricanes. He was also a full participant at February’s Scouting Combine.

Williams enters a good situation in San Francisco, which is likely to lose starting nose tackle Aubrayo Franklin in free agency. Isaac Sopoaga, a far less effective player than Franklin, is currently penciled in as the Niners’ new starter.