Haggans, 35, did not play in the 49ers' first two games.
Starters Aldon Smith and Ahmad Brooks are the only outside linebackers to play for the 49ers to this point in the season. The team has played mostly in hits sub packages while defending the pass-oriented personnel for the Green Bay Packers and Detroit Lions.
Among 49ers backups, Haggans has been the only true outside linebacker on the roster. He cannot play against the Minnesota Vikings, New York Jets or Buffalo Bills. Haggans can return for a Week 6 game against the New York Giants. The 49ers open their division schedule against Seattle the following week.
The possibility of a suspension stemming from a DUI arrest likely influenced the Arizona Cardinals' decision to release Haggans following five seasons with the team. The Cardinals kept Quentin Groves instead. Groves collected a sack and set up a touchdown by blocking a punt during Arizona's 20-18 victory at New England.
The Cardinals needed reliable insurance at outside linebacker because their starters, Sam Acho and O'Brien Schofield, were less established than the 49ers' Smith and Brooks. Schofield continues to battle knee issues. Acho played all the defensive snaps against the Patriots. Schofield played 80 percent. Groves played the remaining 20 percent.