Gettis underwent an MRI exam, according to Rivera, and the Panthers will have more conclusive results of the injury "in about a week" when the swelling in his knee goes down. Still, Gettis likely will miss the season.
"It's disappointing because the young man really showed," Rivera said. "He had a good last few days. He's got a bright future. Whatever it entails, he'll get it right and we'll have him ready to go when he's ready."
Gettis injured his knee Wednesday night and was carted off the field after practice. He injured the knee while attempting to run a route.
"It was down in the red zone, and he was releasing and he got jammed," Rivera said. "His foot got caught and slipped in a bad direction. It's disappointing. Like I said, the young man was having a really good camp."
Gettis had battled back to get on the field after missing portions of training camp with a hamstring injury. The sixth-round draft pick, who had 37 receptions for 508 yards and three touchdowns in 15 games as a rookie last season, was competing for a starting spot opposite Steve Smith.
With Gettis out of the lineup, the Panthers are expected to turn to Brandon LaFell, a third-round pick last year, to compete with Legedu Naanee, a former San Diego Charger who's familiar with the team's offense.
Earlier in the night, the Panthers placed defensive tackle Ron Edwards on season-ending injured reserve and replaced him with free-agent defensive tackle DelJuan Robinson, who played 27 games with three starts in three seasons with the Houston Texans. Edwards, who received a three-year, $8.5 million contract, tore his triceps in his first practice with the team Aug. 4. It was expected at the time that the Panthers would place him on IR.
The Associated Press contributed to this report.