Alonso (knee) and a conditional fifth-round pick were traded from the Saints to the 49ers in exchange for linebacker Kwon Alexander (ankle) on Monday, Tom Pelissero of NFL Network reports.
Alonso has been on the PUP list all season while recovering from ACL surgery at the start of 2020, though he did return to practice a couple weeks ago. The 30-year-old had 31 tackles and played only 290 defensive snaps in 13 games for New Orleans last season, so even once activated, he may not have a major role for San Francisco.