Manager Ron Roenicke said Narveson, who is 8-6 with a 4.49 ERA, apparently raked the thumb across the screw that held the scissors together.
Roenicke said Zack Greinke, who had been scheduled to start Saturday on five days' rest against the Pirates, could be moved up to take Narveson's spot on Friday against Pittsburgh. Marco Estrada and Frankie De La Cruz, who is at Triple-A Nashville, could take Narveson's spot in the rotation.
Estrada has appeared in 32 games with four starts and was 2-7 with a 4.80 ERA. De La Cruz was 7-6 with a 3.88 ERA in 25 games, all but two of them starts, in the minors.