Practice summary: Linebacker Darius Fleming, who missed his rookie season with a torn ACL in his left knee, appeared to sustain a serious injury on the same knee during a non-contact kickoff coverage drill during Sunday's practice.
Fleming fell to the ground and was assisted by the 49ers' staff of athletic trainers as teammates tried to console him. There was no immediate word on Fleming, who was activated off the physically-unable-to-perform list on Thursday. Fleming began camp on the PUP list after re-injuring his left knee in the 49ers' offseason program on June 4.
Fleming, whom the 49ers drafted in the fifth round of 2012, was moved from the outside to inside linebacker this offseason.
Training camp is appearing to take a physical toll on the 49ers, as the full team held its fourth consecutive day of practice. The 49ers have a much-needed day off on Monday.
[RELATED: Harbaugh -- Okoye plays better in pads]
Receiver Kyle Williams, who sustained a hamstring strain on Saturday, did not practice. Receiver Ricardo Lockette appeared to experience discomfort in his right hip. He continued to hobble through practice. Also, receiver Marlon Moore came up lame after running a deep route. He also remained in the remainder of practice.
Quarterback Colin Kaepernick began strong during seven-on-seven drills with some beautiful downfield throws to tight ends Garrett Celek and Vance McDonald. The pass defense made more plays during the 11-on-11 sessions of practice.
Cornerback Tramaine Brock intercepted one of Kaepernick's passes, as his throw intended for A.J. Jenkins was tipped at the line. Linebacker Michael Wilhoite dropped a Kaepernick pass aimed at slot receiver Chad Hall.
Hall and Anquan Boldin had active days with four receptions apiece during 11-on-11 drills.
Offensive play of the day: Kaepernick showcased his big arm when he drove a deep seam route for Celek. Safety C.J. Spillman, who ran with the first-team defense on Sunday, had good coverage underneath the route. But Kaepernick's pass whizzed just over his finger tips and settled nicely into Celek's mitts about 30 yards down the field.
Defensive play of the day: Rookie safety Eric Reid had his eyes on quarterback Scott Tolzien and made a well-timed break on an intermediate route to get in front of Celek for his first interception of training camp. Reid also made another strong play late in practice when he broke up a Kaepernick pass intended for Boldin.
Rookie report: WR Quinton Patton was again off-limits for all passes. Patton is wearing a soft cast over his left index and middle fingers. He ran routes at full speed but the ball never came his way. Coach Jim Harbaugh said Patton has a "jammed finger." . . . B.J. Daniels took part in blitz pickup drills with the running backs. He matched up once against LB Nate Stupar and fared OK. But he had two rough repetitions against LB Nick Moody, who plowed over him. . . . McDonald matched up very well in pass protection against OLB Corey Lemonier. McDonald made a nice catch of a deep seam route from Kaepernick in 11-on-11 drills against the coverage of SS Donte Whitner. McDonald also had a catch along the sideline against Fleming's coverage.
Flag football: LaMichael James, Chuck Jacobs, Daniels, Hall, Jenkins, Darryl Morris and Perrish Cox donned belts with flags attached for a kickoff drill in which two coverage players converged down the field. That was the drill in which Fleming sustained his knee injury.
Competition to watch: Nose tackle Ian Williams had another strong day, as he got constant penetration while working on the 49ers' No. 1 defense. Glenn Dorsey, who is competing with Williams for the starting job, batted down a pass at the line of scrimmage.
On the sideline: Williams (hamstring) did not practice. WR Michael Crabtree (Achilles), RB Kendall Hunter (Achilles), WR Mario Manningham (knee) are on the active PUP list. RB Marcus Lattimore (knee), DE Tank Carradine (knee), DT Quinton Dial (toe) and OT Luke Marquardt (foot) are on the active non-football injury list.
Quote of the day: "It was impressive that he got the pads put in all the right slots. He was off to a good start."
--49ers coach Jim Harbaugh on Lawrence Okoye's first padded practice