Dahl's agents at Sosnick Cobbe and Karon announced the decision in tweets Sunday night:
.@ddahl21 has made the difficult decision to have his spleen removed tomorrow. Doing so allows him to return (1/2)
(2/2) this season instead of next year, though it also brings other challenges. #Courage #Prayers #RonnieLott1986 #Rockies #MiLB
— Sosnick Cobbe Karon (@SosnickCobbe) May 31, 2015
The agency announced the surgery on Sunday night.
Dahl, 21, was Colorado's top pick (10th overall) out of Oak Mountain High School near Birmingham, Ala.