Crabtree, San Francisco's leading receiver in 2012, underwent surgery after tearing the tendon during a practice on May 21 and is still in the early stages of rehabilitation.
The 49ers, however, aren't ruling out Crabtree returning at some point during the season.
"I wouldn't categorize it as 'ahead of schedule' because he is just starting to move on it," Harbaugh said Monday. "It's just been healing but it looks great. That's from the words of the doctors, so, again, optimistic there."
Veteran Anquan Boldin will start at one of the wide receiver spots, while A.J. Jenkins, Ricardo Lockette, Quinton Patton and Marlon Moore are among the group competing for the No. 2 spot with Crabtree sidelined. Veterans Kyle Williams and Mario Manningham, both recovering from ACL injuries, likely will begin training camp on the physically unable to perform list.
"I really feel like they're making a lot of progress," Harbaugh said of the receivers vying to start opposite Boldin. "I feel good about where that stands right now."
Information from The Associated Press was used in this report.