O'Brien (forearm) has been long-tossing as he continues a throwing progression, Daniel Guerrero of the St. Louis Post-Dispatch reports.

O'Brien (forearm) was moved to the 60-day injured list Friday, John Denton of MLB.com reports.

O'Brien (forearm) will begin a throwing program this week, Katie Woo of The Athletic reports.

O'Brien (forearm) underwent an MRI on his right flexor tendon Monday, John Denton of MLB.com reports.

O'Brien was placed on the 15-day injured list Sunday with a flexor strain in his right forearm.

O'Brien has allowed three hits and struck out two without walking a batter over three scoreless innings in Grapefruit League play.

The Cardinals acquired O'Brien from the Mariners for cash considerations and purchased his contract from Triple-A Memphis on Monday, Derrick Goold of the St. Louis Post-Dispatch reports.

O'Brien cleared waivers and was outrighted to Triple-A Tacoma on Thursday.

O'Brien was designated for assignment by the Mariners on Friday.

The Mariners optioned O'Brien to Triple-A Tacoma on Sunday.