Coveted Rockies pitching prospect Eddie Butler will make his big-league debut Friday, replacing Franklin Morales, who moved to the bullpen Tuesday, a team source said.

Morales went 0-3 last month and his ERA ballooned to 6.03 — the worst mark in the majors among starting pitchers. After a six-run effort in a loss at Cleveland last week, Morales was told he would be moved to the bullpen, a team source said.

He was available as a reliever Tuesday against Arizona.

Morales’ next start was scheduled for Friday in Denver against the Dodgers, but that spot will be filled by Butler, a right-hander currently with Double-A Tulsa, according to a major-league source.

Butler (4-4, 2.49 ERA with the Drillers) struggled in his last start, pitching 42/3 innings Saturday, allowing seven hits and two earned runs against the Midland (Texas) RockHounds.

But Rockies manager Walt Weiss recently said Butler was ready for the big leagues.

“If he’s not, then he’s real close,” Weiss said. “I don’t think there’s a lot of development left. It’s just the experience of being here. That’s obviously what he lacks. But as far as developing a pitch or more command, I think the development is behind him.

“It’s tough to make a black and white statement because he hasn’t pitched at this level. Stuff-wise? I don’t think there’s any doubt,” Weiss said of Butler.

Butler will be the first Rockies pitcher called up directly from Double-A since Chad Bettis in 2013. Bettis went 0-3 in eight starts after joing the Rockies in August before he joined the bullpen.

Juan Nicasio, too, jumped from Double-A Tulsa to the Rockies in late May of 2011. He went 4-4 in 13 starts that season.

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