Ponson, 31, will report to Triple-A Scranton/Wilkes-Barre. He was designated for assignment by the Texas Rangers on June 6 and was 4-1 with a 3.88 ERA in nine starts for Texas, but a series of off-the-field incidents prompted the Rangers to drop him from the team.
Yankees general manager Brian Cashman said that the club's recent injury concerns prompted the signing. New York suffered a hit to its Major League rotation this week when right-hander Chien-Ming Wang, who leads the Major Leagues with 46 victories since the beginning of the 2006 season, was lost until at least September with a right foot injury.
Dan Giese is set to make Saturday's start against the Cincinnati Reds in Wang's place. The Yankees will need a starting pitcher for their split doubleheader on June 27 against the Mets, and it is conceivable that Ponson could progress to make one of those starts.
"I just think it's an obvious move," Cashman said.
Though he had a solid performance on the field this year, Ponson was available as a free agent because of events that transpired away from the ballpark. Ponson was reportedly put on notice after creating a serious disturbance at the hotel bar in St. Petersburg, Fla., during the Rangers' recent road trip and was told that further problems would not be tolerated.
He also reacted furiously after being taken out of a June 4 game against the Indians and with being pushed back from the start that was to follow that outing, prompting Rangers general manager Jon Daniels to say, "We don't feel Sidney deserves to be here or wants to be here."
Cashman said he spoke with Ponson on Wednesday and expected that he would try to put those issues behind him, looking at the Yankees as a new opportunity.
"Whatever happened in Texas, hopefully stays in Texas," Cashman said. "He's looking forward to putting himself in a position to help us out."
Ponson has a career record of 86-102 and a 4.90 ERA in 268 Major League games for six organizations, including a brief stint with the Yankees. He appeared in five games (three starts) for New York at the end of the 2006 season, going 0-1 with a 10.47 ERA.
"At that point in time, the performance didn't follow," Cashman said. "My understanding is how he was throwing in Texas was considerably better than how he was throwing when he was here in '06. Hopefully, we'll see stuff like that in Scranton and we'll make a decision. If it doesn't work out, it doesn't work out."
The Yankees also announced Wednesday they have claimed right-handed pitcher Oneli Perez off waivers from the Cleveland Indians and optioned him to Double-A Trenton.
Grinning with a nod toward the Yankees' rumored interest in C.C. Sabathia, Cashman said, "I got a pitcher from Cleveland like you've all been expecting."
Perez, 24, has appeared in 21 games combined this season at Triple-A Charlotte (White Sox) and Triple-A Buffalo (Indians), going 0-1 with two saves and an 8.49 ERA in his first action at the Triple-A level.
In order to make room on the 40-man roster, the Yankees transferred right-handed pitcher Jonathan Albaladejo to the 60-day disabled list.
Bryan Hoch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.