The Phillies placed Halladay on the 15-day disabled list on Tuesday with a strained right latissimus dorsi. The two-time Cy Young Award winner will be sidelined from baseball activities for three weeks and is expected to be out from six to eight weeks.
Halladay, who was 4-5 with a 3.98 ERA before the injury, is expected to address reporters sometime during this weekend's series against the Marlins at Citizens Bank Park.
"We'll probably know more, hopefully we'll have an update for you guys [on Friday] once we get all the information," Amaro told MLB.com on Thursday during Hunter Pence's "Let's Go Eat: Food and Fun Fest" charity event.
"We don't anticipate a whole lot of a difference, but of course you always get nervous about what other doctors may say about his situation. But we feel pretty confident that it will be a situation where we don't have to worry about any surgeries. I hope."
The Phillies have yet to announce a starter for what would have been Halladay's next outing, on Monday against the Dodgers. It's possible that Vance Worley, who is on the 15-day DL with inflammation in his right elbow, could be activated in time to make the start on Monday. Worley will throw a bullpen session on Friday.
"We feel like if he gets through that well, then I think what's going to happen is, he'll probably slide into that slot," Amaro said. "But again, it remains to be seen. [We'll] see how it goes [on Friday]."
As for Chase Utley and Ryan Howard, Amaro said the two are progressing each day, though there is still no timetable for either to return.
Asked on Wednesday in New York if Howard is likely to return before July 1, Amaro said, "I don't expect it."
"I know that Ryan does a little bit more each day, and I know that Chase has been feeling better and better, I think, every day," he said on Thursday. "It's one day at a time. It's a process, but hopefully we can get those guys playing in games sometime soon."
Jake Kaplan is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.