PHOENIX -- With starter Barry Enright being optioned to Triple-A Reno on Thursday, the question is: Who will take his spot in the rotation?

The answer: TBD

The D-backs will not need to fill that spot in the rotation until May 14, when they take on the Dodgers in Los Angeles, and D-backs manager Kirk Gibson did not seem to be in a rush to make a decision.

"There are different scenarios," Gibson said. "You find out things can change. We're just going to wait and see how things develop."

Certainly a leading candidate has to be Josh Collmenter, who is 1-0 with a 1.46 ERA in six relief appearances. Collmenter, a starter throughout his Minor League career, has pitched out of the bullpen since being called up from Reno on April 15.

"I'm sure he would be," Gibson said, when asked about Collmenter being a candidate. "He just gets people out."

For him to be a successful starter, Gibson said Collmenter would need to improve his curve so that it complements his fastball and change.

One person who is not a candidate is Aaron Heilman, who tried to win a spot in the rotation this spring. The club prefers to keep him in the pen for now.

Heilman activated from disabled list

PHOENIX -- Reliever Aaron Heilman was activated from the disabled list Thursday, where he had been since April 15 with shoulder tendinitis.

It was the first time the D-backs right-hander had been on the DL in his nine big league seasons.

After spending the last five years in the bullpen, Heilman attempted to make the rotation this spring, but lost out to Armando Galarraga for the No. 5 spot. He said that the added innings he pitched during the spring was not a factor in his injury.

Heilman threw a simulated game, and also appeared in an extended spring game before being declared ready.

"I've been progressing along each time I was going out there and [I] feel real good, ready to go, anxious to go back out there," said Heilman, who had a 12.15 ERA in four games before going on the shelf.

Enright optioned to Triple-A Reno

PHOENIX -- When he was told Thursday afternoon that manager Kirk Gibson wanted to see him, Barry Enright knew the news would not be good.

It was not.

Enright was optioned to Triple-A Reno, as the club activated reliever Aaron Heilman from the disabled list.

After a strong spring earned him the No. 4 spot in the rotation, Enright has struggled to a 6.49 ERA in six regular season starts. He appeared to be turning a corner in his start last week against the Cubs, but could not build on that as he allowed six runs in five innings vs. the Rockies on Wednesday.

Enright has had trouble finishing off innings. Of the 25 runs he's allowed this year, 16 have come with two outs, including all six Thursday.

"Obviously, a lot of two-out runs this year and [Gibson] said go down and we want to see the same guy we saw at the beginning of last year, and the beginning of games this year," Enright said. "This is extra motivation, a bump in the road, and hopefully I'll be up here soon."

In his first 12 big league starts last year, Enright compiled a 2.45 ERA, while in his final five he had an 8.06 mark.

"He's certainly one of my favorites," Gibson said. 'He understands what he has to do. I don't think it's anything mechanical. I think part of it is just confidence. We all saw what he could do last year in his first 12 starts."