Reymond Fuentes pinch-ran for Cedeno. Then Alexi Amarista moved from center field to shortstop, with Fuentes moving to center field, in the top of the eighth.
Cedeno was attended to by the training staff but never fell to the ground.
"He's a little woosey," Padres manager Bud Black said. "He's got a little bit of a headache. It hit him pretty square. We'll monitor him overnight."
Cedeno has been a pleasant surprise since taking over at shortstop for the Padres' lone All-Star, Everth Cabrera, who was suspended last month for the final 50 games of the regular season for violating baseball's drug policy.
Cedeno is hitting .242 with three home runs and 21 RBIs this season, including .275 with two home runs and nine RBIs in 37 games entering Monday.
Bell was apologetic after the game.
"I feel bad. I tried to apologize, and I actually texted their head trainer over there and told him I didn't mean to and ask him how he was. He said he was OK, just a little fuzzy," Bell said. "I was trying to throw a sinker down the middle and the ball just got away. I mean I never want to hit someone in the head like that, even if I was really [mad] at him. Ronnie didn't do anything. It was just an accident, but that's why we wear helmets."