Utley has been out with chondromalacia (soft cartilage under the knee cap) in his left knee, while Howard is in Clearwater, Fla., rehabbing from surgery on his left Achilles tendon.
"I don't think the player knows, I don't think our doctors know and I don't know when they're going to be back," Amaro said. "Hopefully soon, as soon as possible.
"They're both getting better every day it seems."
Amaro said he did not know if one player was ahead of the other in their rehab. Utley has been with the club and has taken ground balls in batting practice a few times in the last week.
"I don't know, because Chase could come to me and say, 'I'm ready to go play some games right now,'" Amaro said. "I don't know that, because I don't know how he feels on a day-to-day basis. It changes. So all I know is right now he's progressing. He's doing more things than he did a couple weeks ago. That's all we can kind of go by."