Crabtree had a big game, catching nine receptions for 119 yards and two touchdowns.
Crabtree has not been arrested or detained for anything and is still expected to play in Sunday's NFC Championship game against the Atlanta Falcons on Sunday.
The San Francisco Special Victims Unit is looking into the allegations and Crabtree has already been interviewed with his lawyer present. The San Francisco Chronicle reports that Crabtree has agreed to cooperate with the police and make himself available for future interviews.
The 25-year-old receiver had his long awaited breakout year for the 49ers, catching 85 receptions for 1,105 yards and nine touchdowns during the regular season.