San Francisco 49ers linebacker Clark Haggans has been suspended for three games by the NFL for violating the league's substance abuse policy, the 49ers announced Tuesday. Haggans was signed by the 49ers on Sept. 2 after he had been released by the Cardinals. His suspension apparently stems from a drunken-driving conviction in June. The suspension will start immediately, and he will be eligible to return the day after the 49ers' Oct. 7 game against the Buffalo Bills. "Earlier today the team was made aware of the NFL's decision to suspend Clark Haggans for three games," 49ers general manager Trent Baalke said in a statement. "We were certainly aware that this decision was a possibility as we evaluated Clark prior to adding him to our roster. Therefore, we are prepared to move forward accordingly." Haggans did not play in either of the 49ers' first two games.