From the official site:

Ponson, 29, was designated for assignment last week by the Cardinals, then released on Thursday. Yankees general manager Brian Cashman said on Thursday that he expected to have Ponson signed and in uniform when the Yanks resume their schedule on Friday, though Ponson won't start for New York until Tuesday against the Mariners.

"We'll take a look," Cashman said. "He's got a good arm. We had two looks at him this year with scouts in the park and obviously a lot of video that we compiled in our library from this year. We assessed this was a shot worth taking."