Herrera has not played since March 12. He originally hurt himself sliding headfirst into home plate on March 6.
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"I kind of thought he'd be further along than he is," Mackanin said.
That is troubling with Opening Day two weeks away. The Phillies already are without Aaron Altherr, who will miss four to six months following left wrist surgery, and Cody Asche, who has not played this spring because of a strained right oblique. They can hardly afford to lose Herrera, too.
"He says he still feels something there," Mackanin said. "Yeah, I'm concerned about it. I don't want to say it's more than it is, but he might just be on the cautious side as well. If he's not our best hitter, he's one of our best hitters. I want to make sure he's healthy going into the season."
If Herrera can get healthy before Opening Day, he is expected to start alongside Peter Bourjos and Rule 5 Draft pick Tyler Goeddel. At the moment, non-roster invitees David Lough and Cedric Hunter could be the fourth and fifth outfielders. But the Phillies are exploring the possibility of acquiring some outfield help.
Arm feeling better, Hernandez returns to hill
David Hernandez allowed two hits, one run and struck out one in one inning of Monday's 4-3 victory over the Tigers in a Grapefruit League game at Joker Marchant Stadium. It was his first appearance in a big league game since March 1 because of right triceps tendinitis.
"It's definitely nice just to see a crowd," Hernandez said. "I felt like I made some good pitches -- progress. I fell behind against the two batters that got extra-base hits."
Hernandez allowed three hits, three runs, one walk and struck out four over two innings of two Minor League games last week. But despite just two big league appearances, the Phillies said he will be ready to open the season in the bullpen.
"I liked what I saw," Phillies manager Pete Mackanin said. "It was good to see him back healthy."
But what will Hernandez's role be? He entered camp the favorite to close based on the fact he is the only free agent the Phillies signed to a Major League contract in the offseason. But at the moment, non-roster invitee Andrew Bailey is the favorite. Bailey has thrown four scoreless innings over four Grapefruit League games.
"We're in the process of trying to figure that out," Mackanin said about bullpen roles. "It might take until the end of the spring, but we'll eventually make it."
"I just want to be healthy, get outs and do whatever I can to help the team win," Hernandez said. "I feel like it's how we all are. Not a lot of people are giving us a chance to do anything this year."
The Phillies optioned right-hander Colton Murray to Triple-A Lehigh Valley before the game. The 25-year-old had a 1.69 ERA in five appearances this spring. He had a 5.87 ERA in eight appearances last season for the Phillies.