The 49ers did plenty of homework in their search for a new defensive coordinator, reportedly promoting Nick Sorensen to the position after he spent two years as an assistant coach.

But San Francisco and New York Jets DC Jeff Ulbrich shared mutual interest in a union, The Athletic’s Zack Rosenblatt reported Monday, citing multiple league sources. And while the 49ers never requested a formal interview, the Jets made it clear they would block Ulbrich from leaving, per Rosenblatt.

While the Jets’ offense has struggled in recent seasons despite quarterback Zach Wilson’s best efforts, the defense under Ulbrich has been top-notch, ranking second in the NFL in opponent yards per game in 2023. But, even with a fully healthy Aaron Rodgers on the horizon for New York, it certainly would make send for Ulbrich to have interest in joining San Francisco, fresh off its fourth playoff appearance in five seasons.

Instead, the 49ers went back to their DC roots with another internal hire in Sorensen, also adding Brandon Staley to the coaching staff as assistant head coach. The DC vacancy came about after 49ers coach Kyle Shanahan fired Steve Wilks after San Francisco lost Super Bowl LVIII.

Bruce Irvin doesn't seem to like former Seahawks going to the 49ers….

'Permanent opps 4life!!' pic.twitter.com/xstrDYmSp2

— Sports ON Tap Seattle (@SeattleONTap) March 5, 2024

Ulbrich, whom the 49ers drafted No. 86 overall in the third round of the 2000 NFL Draft, played linebacker for San Francisco until he retired after suffering a concussion in 2009. He has been coaching since 2010, spending time with the Seattle Seahawks, UCLA, Atlanta Falcons and, most recently, the Jets since 2021.

Sorensen’s promotion, meanwhile, from 49ers passing game specialist/nickel backs coach ended a 17-day search for a new DC after San Francisco also interviewed Staley, defensive backs coach Daniel Bullocks, Kansas City Chiefs defensive backs coach Dave Merritt and Las Vegas Raiders safeties coach Gerald Alexander for the position.