The 33-year old former Manchester United midfielder makes his way from Bahia to sign a loan deal with the Union who have released 23-year old forward Adu who has subsequently joined the Salvador-based outfit.
World Cup winner Kleberson will join the team pending reception of his US working visa, International Transfer Certificate (ITC) and a medical examination and will occupy a Designated Player and international roster spot.
"We're excited to have a player with his kind of experience join an already talented roster," manager John Hackworth said.
"Kleberson has had success at the world's highest level of competition - both on a club and international level - and we hope he can add another dimension to our team.
"We would like to thank Freddy Adu for his service to the Union over the past two years and wish him the best of luck as he continues his career in Brazil.”