Spicer, a fifth-year senior, entered training camp projected to start in the position left void by the departure of Fili Moala, a second-round pick in the NFL draft by the Indianapolis Colts. Spicer was hurt late in practice during a team scrimmage drill and required assistance off the field.
Coach Pete Carroll described the injury as a severe sprain.
"It's not like he's going to just brush this off," Carroll said.
Spicer's absence, and the coaching staff's need to evaluate new players, is expected to provide the 24-year-old Fangupo with an extended opportunity to work with the first-team defense.
The 6-foot-2, 330-pound junior is a transfer from Mt. San Antonio College. He attended Santa Ana Century High and then served a Mormon mission before resuming his football career.
On Wednesday, during the Trojans' first practice in full pads, Fangupo cut down Joe McKnight as the speedy tailback attempted to change direction for the start of what was developing into a big play.
The hit brought celebratory shouts from teammates and coaches. "He's as potentially good as anyone we've had play the three-technique spot," Carroll said.
Senior linebacker Luthur Brown completed a class and received a grade that could make him eligible to begin practicing, Carroll said.
If Brown is cleared to play, he could provide valuable depth for a linebacker unit thinned by departures to the NFL.
Cornerback Shareece Wright, who sat out the last two practices because of a knee bruise, also is finishing summer course work that could affect his eligibility, Carroll said.
Incoming freshman safety Patrick Hall, awaiting academic clearance from the NCAA, was on campus.
Freshman linebacker Jarvis Jones did not practice because of headaches, Carroll said. Redshirt freshman Nick Perry returned after missing several days because of a concussion. . . . The Trojans will practice today at 9 a.m. and 4 p.m.