A junior, Armstead was held out of Baylor's win over Lamar last week for unspecified reasons. He was a preseason All-Big 12 selection and recorded five catches for 62 yards and a touchdown in 27 career games.
The top backup is LaQuan McGowan, a 6-foot-7, 410-pound converted lineman who earned offseason fame for his touchdown catch in the Cotton Bowl against Michigan State. McGowan has not recorded a catch this season.
Armstead's dismissal is one of several disciplinary issues Baylor has already faced this season. Defensive end Shawn Oakman and safeties Orion Stewart and J.W. Ketchum received suspensions for the Bears' season-opening win at SMU. Offensive coordinator Kendal Briles and receivers coach Tate Wallis were suspended by Baylor for the Lamar game for an NCAA recruiting violation.