ATLANTA -- Brandon Morrow will not be in the Mariners' bullpen on Friday night, and his status is uncertain for the rest of the weekend series against the Atlanta Braves.

Morrow, who had moved into the closer role with J.J. Putz on the 15-day disabled list (right elbow), is suffering from back spasms and didn't make the trip to Atlanta.

"We felt rather than make the long flight [on Thursday], he'd felt he might feel better in the next day or two and be able to get on a flight," interim manager Jim Riggleman said before his first game. "I'm not sure when that will be. I think it's literally day-to-day when he might be able to get on a plane."

Morrow's absence -- even temporarily -- is another blow for the struggling Mariners. The righty has a 0.90 ERA and two saves in 24 appearances.

Morrow hasn't allowed an earned run in his last 11 1/3 innings and hasn't been scored on in his past nine frames.He has struck out 15 and allowed just one walk and one hit during the scoreless streak.

The 23-year-old started the season in the Minors because of a tired right arm, but was recalled from Double-A Jackson on April 17.

Morrow, selected by the Mariners in the first round of the 2006 First-Year Player Draft, appeared in 60 games out of the bullpen last year as a rookie. He was 3-4 with a 4.12 ERA.