SANTA CLARA -- Linebacker Darius Fleming suffered a potentially serious left knee injury at 49ers practice on Sunday.

Fleming, who missed all of last season with a torn anterior cruciate ligament in the left knee, was working on kick return coverage when he went to the ground in pain.

He was racing down and seemed to injure himself as he tried to stop directions in pursuit of returner Chad Hall. Fleming lay on the ground briefly before it was obvious that he was in pain and teammates and trainers began to surround him.

A 2012 fifth-round pick out of Notre Dame, Fleming was injured last season during rookie mini camp. He also injured the same knee during this year's mini camp in June, but that injury was not serious.

Further information on Fleming's injury was not immediately available.

Wide receiver Ricardo Lockette injured his right hip during practice. He pulled up on a receiving pattern and complained of pain in the hip. He sat out for about 10-15 minutes before returning to practice, but seemed to still be experiencing some pain.

Fellow receiver Kyle Williams did not participate in practice after suffering a hamstring injury on Saturday. Quinton Patton still had a soft cast on his left hand and wore a blue jersey, meaning he wasn't catching passes or participating in contact drills.

Check back here for more on this developing story.

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