MINNEAPOLIS -- The A's injury bug is seemingly doing its best to make its way from the Major League level all the way down to the Minors, where highly regarded pitching prospect Michael Ynoa will shut things down and undergo surgery Aug. 24.

Although the extent of Ynoa's elbow issues won't be known until the time of the procedure, A's assistant general manager David Forst said Friday that the club anticipates ulnar collateral ligament (UCL) reconstruction -- otherwise known as Tommy John surgery, which typically requires more than a year's worth of recovery time.

The surgery, to be performed by Dr. Lewis Yocum, represents a major setback for Oakland's young phenom, who was signed as a 16-year-old to a then-record $4.25 million signing bonus in 2008.

"He's very young, very talented," A's manager Bob Geren said. "I'm sure he'll bounce back fine. It's been a very successful surgery in our industry."

As a pro, Ynoa has pitched just nine innings due to various injuries throughout his brief career. In that time, he's struck out 11 but has also given up five runs on six hits and four walks.

Ankle injury forces A's Rosales to DL

MINNEAPOLIS -- Adam Rosales isn't one to ever really slow down, but Oakland's ultra utility man will have to do just that for the next month after learning he has a stress fracture in his right ankle.

A's assistant general manager David Forst confirmed the diagnosis Friday, when the club placed Rosales on the 15-day disabled list and recalled infielder Steve Tolleson from Triple-A Sacramento.

According to Forst, Rosales initially had an MRI last week that showed his old stress fracture, first suffered during his time with the Reds nearly a year ago.

"All indications were that it was an old fracture," Forst said, "so it was hard to tell if the pain in his ankle was really stemming from that. The pain he was feeling was in a different spot."

Thus, Rosales was simply given a couple days to rest before being inserted into the starting shortstop spot Wednesday in Seattle, where he played just one inning before the ankle forced him to exit the game. The 26-year-old Rosales was subsequently sent to Oakland to see a specialist, who finally determined the pain he was enduring was, in fact, the result of his old stress fracture.

"The only way to treat that is really to rest," Forst said. "Our best guess, at least from what the doctor said, is that we should assume he'll need four weeks or less."

The move represented the 22nd time the A's have used the disabled list this season, which is tied for second most in Oakland history only to the mark of 25 set in 2008. The club currently has a season-high-tying 11 players on the DL.

"It's frustrating," Forst said. "Obviously, there are some injuries that are more frustrating than others. With Rosales, this is just an overuse injury. There's no way to prevent something like this. So this is something he'll be able to deal with and then move on."

In the meantime, Tolleson will likely be given a longer look than was given during his first stint with the A's this year, which saw him appear in just three games. He collected one hit -- his first one as a Major Leaguer -- in four at-bats during that time.

The 26-year-old utility player was batting .332 with nine home runs and 43 RBIs in 80 games with Sacramento. Furthermore, he left the River Cats having hit safely in each of his last nine games, going 17-for-39 (.436) over that stretch.

"He's swung the bat great, and he's been a big part of the offense down there," Forst said. "We're hopeful he comes in and can give some guys a day off here and there, because we know he can play all the infield positions. That's something we'll need as we get down to the grind of the last couple months of the season."

"He's done a fine job with Triple-A," manager Bob Geren added. "We'll get him some action."

Jackson heads to Triple-A, should return soon

MINNEAPOLIS -- Recovering outfielder Conor Jackson is slated to join Triple-A Sacramento on Friday night, a sign that the injured A's player may soon be making his return to Oakland.

Jackson, initially placed on the disabled list with a strained right hamstring July 5, was stationed in Arizona for a handful of weeks before joining Class A Stockton on Wednesday and Thursday. With the Ports, he went 2-for-7 with a double and two RBIs in two games, playing left field in both games.

According to manager Bob Geren, Jackson is scheduled to play nine innings for Sacramento, where he likely won't be much longer if all continues to go well with his rehab work.

Worth noting

Andrew Bailey (strained ribcage-muscle) threw from a distance of 140 feet on Friday. According to manager Bob Geren, all went well, but there is still no return timetable for the A's closer. ... Hurler Tyson Ross, who started the season in Oakland's bullpen before being optioned to Triple-A Sacramento to transform back into a starter, has landed on the disabled list with a strained ulnar collateral ligament in his right elbow. According to assistant general manager David Forst, Ross will need four weeks of rest before being revaluated again.