Richard Sherman is pessimistic about returning to the San Francisco 49ers in 2021, conceding a "miracle" is needed to re-sign with the NFL franchise.

49ers cornerback and Super Bowl champion Sherman is poised to become a free agent at the end of the season, having joined San Francisco in 2018.

Sherman, who won Super Bowl XLVIII with the Seattle Seahawks, returned to form last year – the five-time Pro Bowler earned second-team All-Pro and Pro Bowl honours as the 49ers won the NFC Championship but lost in the showpiece.

However, the 32-year-old star is aware the 2020 season could be his third and final with the 49ers.

"I know the salary cap deal firsthand from dealing with the P.A. and the league," Sherman, who returned in Week 12 after a calf injury had sidelined him since the opening round, said on Thursday. "And I know [the 49ers'] salary cap situation because I've been in direct communication.

"Like I said when I had the conversation [with the 49ers], if there's some miracle that happens, then sure there's an opening.

"But there are 40 free agents, and they'll probably have $30million or less in cap space.

"They have to bring back Trent [Williams] who costs more than $20m [per season]. They have to pay Fred [Warner] who will cost $18m-plus per year. So, anybody who knows the situation understands that."

Sherman has made three appearances this season as last season's Super Bowl runners-up the 49ers sit bottom of the NFC West with a 5-7 record.