"Everything has gone well," Keller told the club's official website.
"The left elbow needed to be cleaned out because it was locking up on me and this was a good time to do it rather than wake up in January not being able to move my arm.
"I'm looking to play in the Gold Cup and will probably join up with the US team on July 1.
"There's a friendly on the 6th and the tournament starts on the 12th."