"He'll be back this season for sure," Reid said. "I'd like to tell you a time on it, but I can't. I don't know what that time is on it."
Even if Curtis is able to return to the field during the season, there is a good chance his performance will be adversely affected. Quarterback Donovan McNabb and tight end L.J. Smith each had seasons derailed by a sports hernia in recent years.
Reid said Curtis "felt tight" after last week's preseason win over Carolina.
"He practiced Tuesday and just felt like he couldn't get up and go full speed," Reid said.
After signing with the Eagles as a free agent last year, Curtis had a career-high 77 catches for a team-best 1,110 yards and six touchdowns.
The Eagles are short-handed at receiver. The team's other starter, Reggie Brown, has a strained hamstring and has appeared in only a handful of plays during the preseason.
Reid said Greg Lewis and Hank Baskett will share Curtis' starting spot in Friday's preseason game against New England.
"It won't be a threat to what we do," Reid said. "Other guys will have to step up for the time that he's out."
Rookie DeSean Jackson will start in place of Brown, whom Reid expects to be ready for the start of the regular season.
Reid said the Eagles aren't looking to acquire another receiver. He said the team is not looking at veteran Joe Horn, who was cut by Atlanta on Tuesday, and wouldn't comment on the possibility of trading for Arizona's Anquan Boldin, who has asked to be traded.
Also, Reid said that right guard Shawn Andrews will start against the Patriots. Andrews recently revealed that he has been diagnosed with clinical depression. He practiced Saturday for the first time since the team's voluntary workouts in June.
"Shawn's going to give it a go, and we'll just see how he does," Reid said. "We're going to try to keep good communication with him during the game and give him an opportunity to play."