The San Francisco 49ers got a lift from rookie receiver Ricky Pearsall, making his NFL debut exactly 50 days after being shot in the chest, but might have lost starting receiver Brandon Aiyuk to a significant knee injury.Pearsall was activated from the non-football injury list on Saturday and was on the field when the 49ers hosted the Kansas City Chiefs in a Super Bowl rematch. He came in for his first play on San Francisco’s opening drive and caught his first career pass late in the second quarter.Video above: 49ers honor officer, surgeon who helped Ricky Pearsall after shootingPearsall’s return proved to be especially important because the Niners were missing their top three receivers after Aiyuk went down late in the first half with a right knee injury.Aiyuk was hit on the knee after making a catch and stayed down for a few minutes. He was helped off the field …