Calero said he feld discomfort in the muscle area above the kneecap.
"It felt weak today," said Calero, who has appeared in 47 games this season. "On Friday, I started feeling it. But today, there were two pitches [to Utley] where my knee felt weak. I'm fine."
Calero is listed as day-to-day.
In 2003, he had surgery to repair a torn right patella.
Gonzalez said before of his past history with the knee area, the team is being extra cautious.
Hopefully it is nothing more than a little soreness from overuse. But if all is well, it will be the team's best interest to have him good to go as soon as possible because the longer he stays on the shelf the more we will see of Pinto in the late innings and who really wants to see that?