San Francisco 49ers running back Marcus Lattimore has decided to retire.

The former South Carolina standout announced his decision in a statement posted on Twitter.
— Marcus Lattimore (@MarcusLattimore) November 5, 2014

Lattimore, 23, spent the 2013 season on the non-football injury list and remained on that list this season. However, he began practicing last week with the hope that he would be able to play later this season.

The 5-foot-11, 220-pound back suffered serious knee injuries in 2011 (ACL and MCL tears in his left knee) and 2012 (right knee) during his time at South Carolina.

"This was a very difficult decision for Marcus and it was clear after speaking with him that he had put a lot of thought into it," 49ers general manager Trent Baalke said in a statement. "He is a high-character young man who has done everything asked of him and more during his time with us and we have a great deal of respect for the strength and commitment he showed throughout the rehab process.

"It has been a pleasure to have Marcus as a member of our team and our community and we are confident that he will be very successful in whichever path he chooses to take in life. We look forward to supporting Marcus and wish him nothing but the best."