Brackett, 25, joins a long list of Colts defenders facing a rehabilitation stint before Indianapolis opens training camp on July 30. He is expected to miss the balance of the team's offseason program, but to be fully recovered for the start of camp.
It is not known when the groin injury occurred.
Among the Colts' key defenders who have been limited this spring are weakside linebacker Cato June (knee), safeties Bob Sanders (arm) and Mike Doss (shoulder) and cornerbacks Marlin Jackson (shoulder) and Jason David (sports hernia). In addition, second-round draft choice Tim Jennings, a cornerback from Georgia, had arthroscopic ankle surgery in the offseason.
A former undrafted free agent, Brackett flourished in 2005, after supplanting Rob Morris as the starting middle linebacker. He amassed 131 tackles, one sack, three interceptions and five passes defensed. He also forced the goal-line fumble by Pittsburgh running back Jerome Bettis late in the divisional-round game that gave the Colts a chance to tie the contest.
Before the '05 season, Brackett started only one game and had principally played as a nickel linebacker and on special teams.
His standout performance in 2005 earned the onetime Rutgers standout, who was scheduled for restricted free agency, a four-year contract extension after the season.
For his career, Brackett has 174 tackles, two sacks and six interceptions in 47 appearances.
Len Pasquarelli is a senior NFL writer for ESPN.com.