Borowski is eligible to come off the DL on April 30, but that's not going to happen.
"He won't be ready for activity [until] after the 15-day period," Soloff said. "We're hopeful it's going to be four weeks total."
Rafael Betancourt is occupying the closer's role in Borowski's absence and has converted each of his first two opportunities. It is assumed that Borowski, who was 2-for-4 in save opportunities before landing on the DL, will retain his job as the ninth-inning guy upon his return.
Soloff said the triceps strain is the only issue Borowski, who has battled major shoulder problems in his career, is dealing with.
As for Westbrook, his strained right intercostal muscle was still bothering him Friday, so team physician Dr. Mark Schickendantz administered a cortisone injection. Westbrook was asymptomatic Saturday, Soloff said.
"If he continues to progress, he'll start playing games of catch mid-to-late next week," Soloff said.
That places Westbrook, who went on the DL on Tuesday, closer to the four-week timetable as well.
Soloff also provided an update on outfielder Shin-Soo Choo, who has been on the 15-day DL all season after having Tommy John ligament replacement surgery performed on his left elbow last September. Choo has been in extended Spring Training camp in Winter Haven, Fla. After playing solely at designated hitter for three weeks, Choo has begun seeing time in the outfield.
Choo played three innings in right field on Wednesday and Friday and will progress to six innings next week. Once he's proven he can handle a nine-inning workload, he'll be ready for a rehab assignment, most likely at Triple-A Buffalo. Rehab assignments for position players are limited to 20 days.
Anthony Castrovince is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.