"It would have been nice to be back a week ago," he said before Wednesday's game against Toronto, his first public comments since he went on the disabled list July 3 with a left oblique strain.
Greinke was to try to throw off the mound "nice and easy" later Wednesday, manager Chip Hale said, "then probably the first full bullpen will be in a couple of days."
Greinke had rounded into his usual form in a series of starts before the injury, reeling off seven consecutive victories. He is 10-3 with a 3.62 ERA.
Asked if he was frustrated by the injury, Greinke said, "that's a perfect word."
"It took a lot more time," he said. "It's just a bad injury where you have to wait for it to heal before doing stuff. I'm used to having stuff bother me all the time and just going through it. But with this one, you can't do that or else it gets worse."
Greinke was hurt when he hit a sacrifice fly early in a June 28 game against Philadelphia. He left the game after feeling something wrong when he returned to the mound the next inning.
Greinke signed a $206.5 million, six-year contract in the offseason, and the Diamondbacks have been cautious with his rehab.
"You don't want to ever push it and then you have to lose him for another month, start from zero," Hale said, "so we'll be careful."
Greinke has input in the recovery process.
"He's the smartest guy I've been around in baseball," Hale said. "He knows his own body as good as anybody. He knows what it takes to be ready for a major league game."
Greinke said he played catch from 120 to 150 feet on Tuesday.
"Yesterday was the first day I threw where I was close to throwing normal," he said. "Every other time was really babying everything."
Greinke declined to give a timetable for his return.
"I don't want to say the perfect plan, because then you expect perfect results," he said, "and I don't want to say a plan that's slower because that's not the goal and then people would think I'm not trying to get back."
He said it's more than likely he will require a minor league injury rehab start or two.