NFL Media's Alex Flanagan reported during the game that she is hearing it would be the 14-year pro's last contest.
The three-time All-Pro defensive lineman said earlier this month he was considering retirement but didn't talk to reporters Sunday. Smith will address his future Monday.
"I'm still going to be upset about the year, but I'm excited for Justin Smith and any other guy that might not be here next year," linebacker Dan Skuta said, per the San Francisco Chronicle. "I'm excited that they got to go out on a win. Might be Justin's last game ever, so just excited for him and happy for this team that we could go out on a good note."
Smith spent the past seven seasons in San Francisco. He complied 613 tackles and 87 sacks in his 14 NFL years.