Bolden sustained the injury in practice March 31, but Purdue did not announce the specifics until Wednesday. The team is not ruling Bolden out for the coming season, though the junior would need to make a speedy recovery to have any chance of playing.
Bolden will undergo surgery, though a date has not been scheduled. He has a redshirt year available.
The 5-foot-9, 194-pound Bolden tore the same ACL in high school and was limited as a freshman at Purdue.
"While obviously we are disappointed, we understand that injuries are part of athletics and not something we can control," Boilermakers coach Danny Hope said in a statement. "We feel for Ralph as a teammate and member of the Purdue football family moreso than we do as a talented running back, and we will support him throughout his recovery.
"Ralph is a proven battler, and we know he will come back and be a key part of our offense in the future."
Bolden finished third in the Big Ten and 55th nationally in rushing average (77.9 yards per game) as a sophomore last season. He ranked second in the conference in touchdowns with 11 and seventh in all-purpose yards (99.7 ypg).
With Bolden out, sophomore Al-Terek McBurse moves into the starting role. McBurse led Purdue in kickoff return yardage (468) last season but had only four rushing attempts.
Adam Rittenberg covers Big Ten football for ESPN.com.