OAKLAND -- With their 40-man roster filled up and needing to find a spot for one of their promising young pitchers, the A’s had to make a tough decision.

Oakland added Daulton Jefferies to its 40-man roster just hours before the deadline to set rosters in order to protect eligible players from the Rule 5 Draft, which takes place at the Winter Meetings on Dec. 12 in San Diego. The spot for Jefferies opened up after right-hander Jharel Cotton was designated for assignment.

Cotton, who turns 28 in January, was on the mend from Tommy John surgery he underwent in 2018. He was hopeful to return to the starting rotation at some point during '19, but he transitioned to a relief role after two rehab starts in order to preserve his innings limit.

Struggles halted Cotton’s chances as a September callup to contribute to the A’s as a reinforcement out of the bullpen when he posted a combined 7.16 ERA over 18 appearances with Class A Advanced Stockton and Triple-A Las Vegas. With the A's entering the 2020 season with more starters than slots available in the rotation, Cotton became an expendable piece in order to avoid the risk of losing Jefferies to another club.

When a player's contract is designated for assignment -- often abbreviated "DFA" -- that player is immediately removed from his club's 40-man roster, and 25-man roster if he was on that as well. Within seven days of the transaction, the player must either be traded, released or placed on irrevocable outright waivers.

The A’s would like to find a way to keep Cotton in the system, but given his superb changeup and previous success in the Majors in 2016 and parts of '17, he stands likely to get claimed by another club looking to get him back to form next season.

Jefferies, the A’s No. 12 prospect per MLB Pipeline, was seen as one of the top eligible players for the Rule 5 Draft after coming off a spectacular season that earned him Oakland’s Minor League Pitcher of the Year Award from MLB Pipeline. The 24-year-old right-hander went 2-2 with a 3.42 ERA, starting the year at Stockton and finishing up with Double-A Midland. In an effort to limit his innings as he returns from Tommy John surgery, Jefferies worked three innings or fewer in 24 of his 26 outings, turning in a supreme 10.33 strikeout-to-walk ratio over 79 innings.

With catcher Jonah Heim (No. 21 prospect) added to the 40-man roster earlier this month, another notable player in Oakland’s system who could garner interest in the Rule 5 Draft is Wandisson Charles. The 23-year-old right-hander, who possesses a 100 mph fastball and posted a 3.89 ERA over 62 1/3 innings, ended the year at Double-A Midland.