Reich said he believes Cain suffered the injury when he was running a vertical route down the field and tried to stop and come back.
Cain, taken in the sixth round of the draft at No. 185 overall out of Clemson, had stood out during training camp by showing his athletic ability to go up and get the ball.
"One of the traits Deon was flashing with some consistency was an ability to really win versus press coverage," Reich said. "So that's good news for him going forward. We know we have something special in Deon Cain. He's a young guy who can develop into a great player. This is obviously a big setback, but you find [out] in this league that's not uncommon and good players find a way of overcoming those obstacles. We're counting on Deon to overcome this one as well."
Receiver was a position of unknowns beyond Pro Bowler T.Y. Hilton coming into training camp for the Colts. Ryan Grant has emerged to take the lead to be the team's No. 2 receiver, but the third and fourth receiver spots, where Cain was definitely in the mix, are wide open.
Reich didn't rule out the possibility of looking outside the team for help at receiver. That might only happen if the receivers currently on the roster struggle. Second-year player K.J. Brent is another receiver who has been impressive so far in training camp and will get a shot at moving up the depth chart.
"We're always evaluating, but right now we're happy with the receivers we have," Reich said. "We're showing good progress. These guys have been working hard, they've earned the right to have their opportunity to step up and fill the gap. It's next man up, as unfortunate as Deon's injury is. We have to maintain that mentality and these young [receivers] have an opportunity to do that. But as the case with every team, you're always evaluating. At the end of the day, you always have to do what's best for the team."
The Colts are also dealing with injuries at running back. Second-year player Marlon Mack, who has been the front-runner to start, is "week-to-week" with a hamstring injury.