The New England Patriots have placed star tight end Rob Gronkowski on the active physically unable to perform list, according to a league source.

Gronkowski has undergone surgical procedures on his back and forearm and is sidelined indefinitely, but is expected to return at some point.

Gronkowski can be activated at any time. If he remains on the list to begin the season, he would be required to miss at least the first six games.

Gronkowski was joined on the physically unable to perform list by wide receiver Julian Edelman (foot surgery), tight end Jake Ballard (anterior cruciate ligament) and offensive lineman Nick McDonald.

The Patriots placed former USC and Canadian Football League defensive lineman Armond Armstead on the non-football illness list. He has a history of heart issues, including a heart attack sustained in college, so that might explain why he was designated this way.

The Patriots also placed safety Kanorris Davis, wide receiver Mark Harrison and offensive lineman Matt Stankiewitch on the non-football injury list.

Follow me on Twitter: @RavensInsider

Aaron Wilson covers the Ravens for The Baltimore Sun.