The team did not say if Jenkins, who was hurt in a team scrimmage Friday night, will need surgery or whether his shoulder might be separated or dislocated.
"You are always concerned any time your player goes down with an injury," coach Mike Smith said in a statement released by the team Sunday night. "One thing I am certain of is that Michael will work very hard to get back on the field as soon as possible."
Jenkins is entering his seventh season. The 6-foot-4 receiver has appeared in 92 games with 235 receptions for 3,007 yards and 18 touchdowns.
Atlanta opens the preseason Friday night at home against Kansas City. The Falcons' regular season opener is Sept. 12 at Pittsburgh.