Geary, 1-1 with a 1.47 ERA in 19 appearances, hadn't allowed a run in his last 10 appearances. The 31-year-old is among the key relievers Cooper usually employs to bridge the gap from the starting rotation to closer Jose Valverde.
Geary took himself out of the game in the eighth inning Thursday at San Francisco. The club waited a day in the hopes that Geary's health would improve.
"I am sore," Geary said Friday. "Pulling myself early yesterday was a smart decision on my part. It gives me enough time to be able to come back and be fully ready to go, rather than trying to mask an injury and possibly have the injury be worse and more severe."
Geary and the Astros do not want the pitcher to risk further injury, and thus the decision was made to put him on the DL for the time being.
"In that case [of pitching through the pain] you tend to throw differently and by the end of the year your shoulder's ailing and elbow's hurting, not because you've thrown more innings but because you're compensating for something else," Geary said. "Going out and giving up four runs proving to everyone I can throw with pain is stupid. Bringing up somebody who's healthy rather than somebody who isn't probably is a good idea."
There's no timetable for Geary's return.
"I've torn my groin before where it was black and blue," Geary said. "[This is] definitely not as severe, but it does hinder the way I throw, and getting myself into a throwing position and driving towards the target, or wherever I'm throwing it, aggravates it."
Geary hopes to begin throwing on flat ground in a day or two to keep his mechanics as they have been these first two months of the season.
"My problem if I don't throw, that's where the mechanics start going sour," Geary said.
Nieve, 25, was 1-3 with a 5.08 ERA in nine games (including seven starts) for Round Rock. He struck out 33 and walked 10 in 33 2/3 innings, and the Venezuela native has kept opposing hitters to a .291 average. Recently moved to the bullpen, Nieve had not allowed a run in 3 2/3 innings, and since making the move has held hitters to an impressive .154 batting average.
"Nieve has a good arm -- we sent him out this spring so he can get some regular work," Cooper said. "He's been throwing the ball pretty well. He's a guy that's got a great arm, needs to get an opportunity. Now, here's an opportunity for him."