PITTSBURGH -- Right-hander A.J. Burnett was diagnosed on Monday with a flexor strain in his right elbow, and the veteran pitcher also received an injection of platelet-rich plasma to abet the recovery he hopes will have him back on a mound.

Estimated time of Burnett's return was set at approximately four weeks.

"We set the bar at four weeks. Could be before, could be after," said an obviously relieved Burnett, who pledged to return to the mound in the wake of "the most positive news that could have come."

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Examinations of Burnett's right elbow by the Pirates' medical staff indicated that the ulnar collateral ligament is intact. Burnett had the right UCL corrected by Tommy John surgery in 2003.

"I was hoping for no bad news. This is the news you wanted to be able to get back on the mound," Burnett said. "Guys come back form this. [Jason] Grilli had it and came back strong."

Then the Pirates' closer, Grilli walked off the Nationals Park mound on July 22, 2013, holding a right forearm throbbing with pain. Grilli was back on the mound for the Bucs on Sept. 4 -- 44 days later.

Grilli did have the advantage of being able to tune up in some Minor League rehab appearances prior to rejoining the Pirates' bullpen. With the current Minor League season ending the first week of September, Burnett's timeframe is more challenging.

But such complications were the furthest thing from the mind of Burnett, whose smile was back along with some peace of mind.

"I'm 100 percent sure I'll be back on the mound," he said. "When this happens, [not pitching again] does enter your mind. But to have the MRI and the words from the doctor, it makes you feel a lot more comfortable.

"If the results were different, it'd be a terrible way to go out. The way I look at it, I'd still have given these guys and this city my heart, the best that I could. I'm very pleased to get the opportunity to hopefully do it again in four weeks."

Burnett did reiterate that he will not return to the mound feeling as he did last Thursday in Cincinnati, prevented by pain from giving his competitive best.

"Getting back on the mound healthy is what i'm going for," he said. "If it's like the other night, I can't take the mound. If I'm not at a level I can compete the way I need to compete -- I just won't. I feel this is a situation where I can get back and compete, without having anything in the back of my mind."

Burnett, in his 17th Major League season and third with the Bucs, was a first-time All-Star this year and is 8-5 with a 3.06 ERA in 21 starts.