San Diego vice president of scouting and player development Grady Fuson confirmed the injury during the Padres game on Wednesday at PETCO Park against the Rockies.
"This one looks like it came out of nowhere," Fuson said. "The nature of the injury looks like it's something that could have happened on one pitch."
Bush, 21, made the conversion to pitcher earlier this season after struggling offensively in his first four-plus seasons as a shortstop in the Padres' farm sysyem.
Bush appeared in six games for the Padres entry in the Arizona League before earning a promotion to Class A Fort Wayne of the Midwest League.
But Bush left his first and only start with the Wizards on Aug. 9 after reporting pain in his right elbow.
"Obviously, it's been recommended that surgery take place," Fuson said. "We don't have a date yet. But I'm sure it will be in the next week or so."
Fuson said the typical timeframe for recovery from Tommy John surgery is 14 months.
Bush had struck out 16 with just two walks in 7 2/3 innings between Arizona and Fort Wayne.
Since Bush -- a former standout pitcher for Mission Bay High School in San Diego -- was building his arm strength to become a pitcher, the Padres were cautious with him.
He reported shoulder pain and later soreness in his biceps and was shut down each time.
"We wanted to make sure before he ever left Arizona that the day after he pitched, he felt good, that after [throwing on the] side after that he felt good, [and the] day after that he felt good. We went through three weeks before he ever went to Fort Wayne," Fuson said.
Draft deadline passes: The Padres weren't able to come to terms with two of their top Draft picks from June's First-Year Player Draft, though they signed pitcher Wynn Pelzer just before the deadline.
The Padres couldn't reach an agreement with third-round pick Tommy Toledo, a prep outfielder from Florida, or their 10th-round pick, shortstop Christian Colon.
Seven of the Padres' 42 Draft picks have not signed professional contracts.
Not signing Toledo -- who will attend the University of Florida -- was a surprise to Fuson, who said that the pre-Draft discussions with Toledo were promising enough for the team to take him in the third round.
"That's the one that concerns us the most. What did we miss? What happened between Draft day and now?" Fuson said. "Everyone has the right to change their mind. But we have been aggressive on all three."
Any third-round selection unsigned by the deadline is not compensated with a "same slot" pick, but rather a sandwich pick the following year between rounds three and four.
Pelzer is a right-hander from the University of South Carolina who suffered a broken kneecap this summer while playing in the Cape Cod League. Colon will attend Cal State Fullerton.
Fitting in fine: When the Padres broke camp in Spring Training, manager Bud Black probably envisioned Geoff Blum playing any number of positions for the Padres this season.
Outfield might not have been one of them, or even if it was, it likely wasn't atop the list of positions the veteran utilityman is accustomed to.
But after playing eight games in left field this month, Blum has become adept at the position he had played just once since 2004.
"We look at Geoff as an athletic player," Black said. "He's versatile. I thought he would be a guy we would feel comfortable putting anywhere on the field. We felt comfortable that he would make the routine plays."
Blum has proved his worth enough in left field -- a position he's had to play since Milton Bradley strained his right hamstring earlier this month -- enough that Black would consider using him there again.
As it stands, Blum will get the majority of playing time at second base. That's where he was playing Wednesday against the Rockies.
"He's a guy who looks as though it comes easier to him than it might most players who might be in a position that's a little unfamiliar," Black said.
On the mound: As expected, right-hander Clay Hensley will start on Thursday for the Padres in the final game of the series against the Rockies.
Hensley -- who arrived late Wednesday from Portland -- will take the spot of left-hander Wil Ledezma, who lasted only 2 1/3 innings in his last start on Friday against the Reds.
Hensley is 1-3 with a 6.18 ERA for the Padres, though he's allowed just three runs over his 11 innings since recovering from biceps tendinitis.
Hensley's command -- something the Padres have been keeping an eye on -- was sharp in his last start for Portland on Friday, when he allowed two runs in six innings with no walks.
The Rockies have announced a change for Thursday, as their announced starting pitcher Aaron Cook has been scratched with a strained muscle in his side. Elmer Dessens makes the start for him.
It was Cook who needed only 74 pitches to earn a complete-game victory over the Padres on July 25.
Friar notes: On Thursday, Padres first baseman Adrian Gonzalez will participate in an online chat on www.padres.com beginning at 2:30 p.m. ... Black said Wednesday that catcher Pete Laforest will likely get the start behind the plate on Thursday. It will be his first action since being recalled from Triple-A Portland on Saturday. ... Bradley continues to undergo treatment on his strained right hamstring. Black insisted that Bradley is not a candidate for the disabled list, but it was doubtful that the outfielder would play on Wednesday or even Thursday. Bradley has one plate appearance -- a walk in St. Louis on Aug 8 -- since Aug. 3. ... Catcher Josh Bard was behind the plate Wednesday against the Rockies, and with a right-handed pitcher on the mound there's a chance the switch-hitter might continue his recent trend of hitting right-handed against right-handed pitchers. Why? Bard won't exactly say, though Black said Bard was seeing the ball better from the right side and that this trend won't likely last much longer. ... Steve Garrison, one of three pitchers obtained from Milwaukee last month for Scott Linebrink, improved to 2-1 for Class A Lake Elsinore, where he allowed one run in seven innings Wednesday. Garrison has a 1.24 ERA in 29 innings.
On deck: The Padres conclude their three-game series against Colorado at 7:05 p.m. PT on Thursday. Hensley, who will officially be recalled prior to the game, will make the start for the Padres. Dessens (1-1, 6.60) will start for the Rockies.
Corey Brock is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.