The USTA handed out eight wild cards into the main draw Tuesday, including to 102nd-ranked Ryan Harrison and 2010 NCAA singles champion Bradley Klahn.
Last year, Baker won his first U.S. Open match since 2005, after a seven-year absence because of a series of operations to his hip and elbow.
In January, he hurt his right knee in Australia. He returned to competitive tennis last week.
He'll be a long shot when the U.S. Open starts Aug. 26, and the roster of U.S. men is filled with them. On Monday, there were no American men in the top 20 for the first time since the ATP computer rankings started in 1973.