"We've seen improvement in every start," Gibson said. "We've showed confidence, but the results aren't there and that means something. We're not going to be able to continue to tolerate four runs in an inning, that's pretty tough when you're playing the Phillies, they don't give up four runs a game. It's a complex situation."
Collmenter cruised through the first three innings Tuesday against Philadelphia but ran into trouble the rest of his outing and allowed six earned runs on nine hits including two home runs.
Through four starts, his ERA sits at 9.82.
"It's coming out of his hand much better," Gibson said. "But can he get back to where he was? That's the question."
The majority of Collmenter's problems have come from lefties, who are batting .340 against him this season.
"Lefties are hitting the ball hard against him and they got on him [Tuesday]," Gibson said. "That's a concern."