The Chelsea fullback, on loan this season to Schalke 04, flew to London for initial examinations and then on to Germany after suffering the injury during Ghana’s opening game at the African Nations Cup finals in Gabon.
He tore the anterior cruciate ligament in his left knee and damaged the inner and outer meniscus, the Ghana FA officials added. Coach Avram Grant blamed the poor surface at Port Gentil for the injury, suffered in the first half against Uganda one week ago.
Rahman will begin rehabilitation with Chelsea in the coming days.
The 22-year-old cost the London club £21.7m in August 2015 and made 23 appearances before Antonio Conte agreed to loan him to Schalke at the beginning of this season.
(Reporting by Mark Gleeson; Editing by Andrew Roche)
