Righty Josh Wall was optioned to Triple-A Albuquerque and Dee Gordon was transferred to the 60-day DL (eligible to be reinstated on Sept. 3) in corresponding moves.
Guerrier has been on the DL with right elbow tendinitis since April 19 after going 0-1 with a 2.70 ERA in seven games to open the season. How the righty's arm holds up will determine whether he will need offseason surgery.
The reliever will be a welcome addition to a short and overworked bullpen. Manager Don Mattingly didn't have much news to report with Jansen, who was scheduled to meet with a doctor on Thursday.
Although he said it's not ideal, Mattingly plans to alternate Brandon League and Ronald Belisario in the closer role based on matchups with Jansen out.
Jansen missed four weeks last year with a similar situation that required blood thinners, and he had a mild episode during Spring Training this year that didn't require him to miss any time. He has 25 saves and a 2.54 ERA this season.
"He's going to have to make sure he understands everything he has to do to make sure he is taking care of himself," Mattingly said. "We need to understand exactly what we should be doing for him to help him take care of himself."
Mattingly said the best-case scenario would be Jansen returning fairly quickly, but he wanted to wait to hear from the doctors before saying just how quick that could be.
League is a year removed from making the All-Star Game as a closer with the Mariners, and Belisario closes when he plays in the Venezuelan Winter League. Belisario, who picked up his first save since 2010 on Wednesday, said he would gladly accept the closer's role and added he likes the feeling of being on the mound in the ninth.
Opening Day closer Javy Guerra, who was sent down earlier this month to work on his command, will be an option out of the bullpen once the rosters expand Saturday.