Colts rookie quarterback Anthony Richardson is seeking a second opinion on his injured throwing shoulder and is expected to miss Indianapolis' Week 6 game against the Jaguars, a source told ESPN's Jeremy Fowler.

The initial belief was that Richardson suffered a Grade 3 sprain to the AC joint in his right shoulder, sources told ESPN on Sunday, but Richardson and the Colts are still gathering information on the injury. He is expected to undergo an MRI and also will receive a second opinion from shoulder specialist Dr. Keith Meister, according to sources.

Richardson's timetable beyond Indianapolis' game next Sunday in Jacksonville is unclear, although a source told ESPN he could be sidelined "a while."

The Colts were still awaiting an official diagnosis on Richardson's shoulder on Monday morning, a team source told ESPN's Stephen Holder.

Richardson was injured in Sunday's 23-16 victory over the Titans after getting tackled on a 4-yard run with 4:39 left in the second quarter. His right shoulder took the brunt of the impact as he fell to the turf, and he immediately reacted by pointing to his shoulder as he lay on the ground.

Richardson did not return to the game and was replaced by Gardner Minshew, who completed 11 of 14 passes for 155 yards and helped the Colts (3-2) hold on for the victory.

It marks the latest health concern for Richardson, the No. 4 overall pick in this year's draft who has left three games early this season because of injury.

Richardson was pulled from the season opener against Jacksonville after taking a hit to his knee and also missed Indianapolis' Week 3 contest against the Ravens after suffering a concussion in the previous game against the Texans.