Diontae Johnson doesn't know exactly what happened. One minute the Pittsburgh Steelers wide receiver was racing upfield early in the third quarter against San Francisco last Sunday with the ball in his hands, the next he was making his way down the tunnel with a member of the training staff, his right hamstring throbbing and his immediate future seriously in doubt. While Johnson believes his hamstring is getting better, he won't play on Monday night when Pittsburgh (0-1) hosts Cleveland (1-0).