Baker left in the first inning of the 5-4, extra-inning loss to the Los Angeles Angels after crashing into the padded wall near the left-field foul line. He made a sliding catch on Josh Hamilton's line drive and braced his collision with his right knee.
Washington said the knee was swollen.
"Right now there is no major damage," Washington added. "It may be a day or so, but he's fine."
Baker, a .297 career hitter against left-handers, was in the starting lineup Tuesday with Jason Vargas on the mound for the Angels. Baker did not have a plate appearance, however.