12:24pm: Renck tweets that Rincon has in fact been designated for assignment.
12:11pm: The Rockies are calling up righthander Esmil Rogers to start today's game against the Giants, and it appears that reliever Juan Rincon may lose his 40-man roster spot according to The Denver Post's Troy Renck (via Twitter). Rincon's name was not included on the pre-game lineup card.
The 31-year-old Rincon has appeared in just one game for the Rockies this year, giving up one run in one inning of work. Colorado re-signed him to a minor league contract over the winter.