Cardinals' ace Chris Carpenter returned to St. Louis yesterday to undergo a series of tests on his neck and shoulder, and will likely begin the season on the disabled list, reports Jenifer Langosch of MLB.com.

Carpenter, who has been dealing with shoulder "weakness" for nearly a month due to a cervical disc bulge in his neck, received no definitive results from his tests yesterday and is expected to undergo further testing today.

The right-hander reportedly threw a strong and pain-free live batting practice session on Sunday but the shoulder weakness returned the following day while playing catch.

Without an answer to what is ailing Carpenter, the Cardinals cannot set a timeline for his possible return to the rotation. Cardinals GM John Mozeliak told Langosch that he excepted answers in the next two days but that Carpenter's return for opening day was "highly unlikely".

As reported last week, reliever Lance Lynn will move into the rotation until Carpenter can return from injury.

• Cardinals' Chris Carpenter shut down; likely to start year on disabled list | MLB.com
  Chris Carpenter will likely begin the season on the DL after returning to St. Louis on Tuesday for tests to determine the cause of his shoulder/neck weakness.

• Kyle Lohse to start on Opening Day | Twitter @LangoschMLB
  With Chris Carpenter sidelined, the #STLCards will give the ball to Kyle Lohse on Opening Day. Adam Wainwright to pitch home opener.