Hernandez, acquired from the Twins off trade waivers Friday, threw a bullpen session Saturday, and will be added to the roster after he passes a physical.
Local reports have suggested right-handed reliever Kip Wells will be removed from the roster to make room for Hernandez, who was 10-8 with a 5.48 ERA in 23 starts for the Twins.
Hurdle wouldn't say anything about the rotation beyond Sunday's start, since the next open spot will come on Friday. Hurdle is intrigued by the presence of Hernandez.
"He's pitched more big games than probably our entire staff put together," Hurdle said. "[He has] the ability to pitch innings, a volume of innings. He's got experience within the [NL] West Division, some success within the West Division."
Hurdle said he presented the move to the bullpen to De La Rosa (5-6, 6.55 ERA in 18 games, 15 starts), who has pitched the Rockies to wins in three of his past four starts, as a chance to help the club in a different manner.
In a brief stint as a reliever earlier this season, De La Rosa struck out five in 4 2/3 innings over three appearances and gave up two runs. The only other left-hander in the Rockies' bullpen is closer Brian Fuentes.
"As we explained to him, we have put a lot of effort into this, as he has," Hurdle said of his discussion with De La Rosa. "Looking at it any other way but as a continued opportunity to continue pitching and making pitches, I think would be exploring the wrong side of the map."
Thomas Harding is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.