The 49ers (7-8) were forced to make a move because kicker Ricky Schmitt went on injured reserve with a left groin problem and regular starter Joe Nedney has been sidelined with a hamstring injury. Schmitt was signed before last week's victory over the Detroit Lions, against whom he made 2 of 3 field-goal attempts.
Andrus tried out with the Colts for the fourth consecutive year. He also was with the Colts in 2006 and 2007, but he only lasted until training camp each time. He signed with the New York Giants in January 2008, but was waived last February after their Super Bowl victory over the New England Patriots and rejoined the Colts two weeks later.
The Associated Press contributed to this report.