Free agency doesn't officially start until March 9, but a two-day window opened on Tuesday for teams to negotiate contracts with free-agent players. If both sides agree to terms, the deal can't be made official until Thursday at 1 p.m. PT.

So as players around the NFL begin to change teams this week, here's a primer of who's on the market. The San Francisco 49ers have plenty of cap flexibility and could potentially target some of these names.

Below are 25 of the most high-profile free agents including a note on their production in 2016.

WR Alshon Jeffrey (Chicago Bears)

2016: Jeffrey played in 12 games, catching 52 passes for 821 yards and two touchdowns.

DE Calais Campbell (Arizona Cardinals)

2016: Campbell started all 16 games and recorded eight sacks, one interception, two forced fumbles, three fumble recoveries and one defensive touchdown. His sack total was his highest since 2013.

DT Brandon Williams (Baltimore Ravens)

2016: Williams logged 51 tackles and one sack in 16 starts.

LB Dont'a Hightower (New England Patriots)

2016: Hightower made his first Pro Bowl after racking up 65 tackles, 2.5 sacks and one forced fumble.

CB A.J. Bouye (Houston Texans)

2016: Bouye intercepted one pass and recorded 16 passes defended in 15 games. He also logged his first career sack. 

G Kevin Zeitler (Cincinnati Bengals)

2016: Zeitler started all 16 games for the second consecutive season.

CB Stephon Gilmore (Buffalo Bills)

2016: Gilmore tallied five interceptions, 12 passes defended and 48 total tackles.

RB Adrian Peterson (Minnesota Vikings)

2016: A knee injury limited Peterson to just 72 rushing yards in three games.

DT Dontari Poe (Kansas City Chiefs)

2016: Poe recorded 1.5 sacks and one forced fumble in 16 starts.

DT Johnathan Hankins (New York Giants)

2016: Hankins played all 16 games and posted three sacks and one forced fumble.

TE Martellus Bennett (New England Patriots)

2016: Bennett racked up 55 catches for 701 yards and seven touchdowns in his only season with the Patriots.

WR Desean Jackson (Washington Redskins)

2016: Jackson notched his fifth 1000-yard season with 56 receptions and four touchdowns.

WR Terrelle Pryor (Cleveland Browns)

2016: Pryor's breakout season included 77 receptions for 1,007 yards and four touchdowns.

S T.J. McDonald (Los Angeles Rams)

2016: In 16 starts, McDonald posted two interceptions and one sack.

OLB Nick Perry (Green Bay Packers)

2016: Perry totaled 52 tackles, 11 sacks and one interception in his fifth season with the Packers.

S Tony Jefferson (Arizona Cardinals)

2016: Jefferson played in 15 games and recorded two forced fumbles, two fumble recoveries, two sacks and 92 total tackles.

LB Zach Brown (Buffalo Bills)

2016: Brown made his first career Pro Bowl after logging four sacks, one interception, two forced fumbles and 149 total tackles.

T Riley Reiff (Detroit Lions)

2016: Reiff made 14 starts last season.

T Ricky Wagner (Baltimore Ravens)

2016: Wagner appeared in 15 games (14 starts).

WR Pierre Garcon (Washington Redskins)

2016: Garcon posted 79 receptions for 1,041 yards and three touchdowns. It marked his second career 1,000-yard season.

DT Chris Baker (Washington Redskins)

2016: Baker started all 16 games and tallied 4.5 sacks, two forced fumbles and 48 tackles. 

DB Micah Hyde (Green Bay Packers)

2016: Hyde intercepted three passes and logged 56 tackles in 16 games (11 starts).

OLB DeMarcus Ware (Denver Broncos)

2016: The future Hall of Fame pass-rusher posted four sacks last season.

CB Logan Ryan (New England Patriots)

2016: In 16 games (13 starts), Ryan recorded two interceptions, 11 passes defended, one forced fumble, one sack and 92 tackles.

WR Brandon Marshall (New York Jets)

2016: Marshall caught 59 passes for 788 yards and three touchdowns last year.