Suddenly, Gophers football coach P.J. Fleck must replace his top lieutenant.

Joe Rossi, a highly regarded assistant who has been Gophers defensive coordinator since late in the 2018 season, is leaving to take the same position at Michigan State, a source with knowledge of the situation told the Star Tribune on Sunday.

Rossi, 44, has been with the Gophers since 2017, taking over as defensive coordinator in the 10th game of the 2018 season and immediately helping Minnesota close the season by winning three of its final four games, allowing 14.8 points per game after Robb Smith's defense gave up an average of 29.9 in the first nine games.

That set the stage for the stage for an 11-2 season in 2019, when the Gophers ranked 10th in total defense and finished No. 10 in the final Associated Press poll.

Under Rossi, the Gophers had one of the top defenses in the nation in 2021 and '22, ranking third in total defense (278.8 yards allowed per game) and sixth in scoring defense (17.3 points allowed per game) in 2021, and ninth in total defense (294.7) and fourth in scoring defense (13.8) in 2022.

This year, the Gophers struggled with inexperience and injuries, giving up 373.8 yards (60th nationally) and 26.9 points (71st) as the team finished 5-7 in the regular season.

"There's always a fine line between playing really good defense and not-so-good defense," Rossi said before the Nov. 25 regular-season finale against Wisconsin. "And I talk to the guys about that all the time. I've been around the block enough times to get through the ups and downs. With that perspective, you never get too high, and you never get too low. Because if you get too high, you get fat and happy and you take things for granted. If you get too low, you lose your confidence."

With Rossi as defensive coordinator, 10 Gophers defensive players have been NFL draft picks, including second-rounders Antoine Winfield Jr. and Boye Mafe. Senior safety Tyler Nubin is a strong candidate to become the 11th.

Rossi's 2023 salary was $1.1 million, and he was due to make $1.15 million next season, the second of a three-year contract. By leaving, he would owe a $330,000 buyout to the school. Michigan State's defensive coordinator this season, Scottie Hazelton, had a salary of $1.19 million, according to the USA Today database of assistant coaches' salaries.

This is the second consecutive year the Gophers have lost one of their coordinators to another Big Ten school. Offensive coordinator Kirk Ciarrocca left for the same role with Rutgers following the 2022 regular season.

Rossi received interest from other programs in previous years. He reportedly was runner-up to Al Golden for the Notre Dame defensive coordinator job after the 2021 season.

At Michigan State, Rossi will join the staff new Spartans coach Jonathan Smith, formerly of Oregon State. The Beavers under Smith were known for their strong defenses, and defensive coordinator Trent Bray was promoted to replace Smith as head coach. That left Smith with a spot to fill at Michigan State, and Rossi leaves the Gophers with a 40-22 record as defensive coordinator.

The Gophers face Bowling Green in the Quick Lane Bowl on Dec. 26 in Detroit, and they will likely have an interim defensive coordinator for that game. One candidate for that role could be Nick Monroe, the cornerbacks coach and co-defensive coordinator. Monroe served as Syracuse's interim defensive coordinator in last year's Pinstripe Bowl against the Gophers, who a few weeks later hired the Mahtomedi native.