SCOTTSDALE, Ariz. — Eddie Butler will pitch Saturday with a big-league roster spot on the line.

Butler, 24, is scheduled to throw an abbreviated outing against the Mariners in the Rockies’ final Cactus League game of spring training at Salt River.

If he does well, Butler will start Wednesday at Milwaukee in Game 3 of Colorado’s season-opening series.

“If he goes out and there are no issues tomorrow, yeah,” Rockies manager Walt Weiss said Friday. “He’d be lined up for that day. We’re looking at that day.”

The Rockies on Friday whittled down their choices for a fourth starting pitcher by reassigning Jon Gray to the minor leagues and moving Christian Bergman into the bullpen.

Bergman will be on the Rockies opening-day roster when they start the season in Milwaukee on Monday, he said. But he will be there as a long-relief option.

“I’ll be the bridge, if they need it,” said Bergman, who will pitch two innings behind Jordan Lyles on Friday night against the Mariners in Peoria. That leaves Butler as the leading option for the Rockies’ starting spot Wednesday against the Brewers.

“We’re expecting him to get relatively deep into the game,” Weiss said.

Butler thought he was pitching Friday, but found out the plan changed when he arrived at the clubhouse.

“That was a little puzzling,” he said.

Butler was pulled from his previous start on Monday after one inning with shoulder fatigue. But he made a quick recovery and was throwing long-toss by Wednesday.

The Rockies can start the season with four pitchers in their rotation and use an off-day Thursday to give everyone regular rest. No. 1 starter Jorge De La Rosa is recovering from a groin injury and won’t be ready to start the season.

With De La Rosa likely headed to the disabled list, Butler and Bergman would give the Rockies a full 25-man roster.

Nick Groke: ngroke@denverpost.com or twitter.com/nickgroke