Mitchell announced his retirement earlier this year after spending the regular season as a free agent. San Francisco was apparently able to lure him back for their playoff game next weekend.
Mitchell, 31, is a former third-round pick of the Texans back in 2010. He spent four years in Houston before signing a four-year, $19 million contract that included $8 million guaranteed with the Dolphins.
The Dolphins released Mitchell in 2017 and he later agreed to a four-year, $16 million contract with the 49ers. He was set to make base salaries of $2.85 million over the final two years of the agreement when the 49ers declined his option this offseason.
The Seahawks signed him back in July as an unrestricted free agent but cut him loose during final roster cuts. He had a workout with the Colts but has remained unsigned.
During his nine-year NFL career, Mitchell recorded 267 total tackles, 6.5 sacks, one forced fumble, three recoveries and nine pass defenses.