The 27-year old winger remains under investigation for allegedly being sexually involved with a 15-year old girl but is on bail and has now been given the all-clear to continue training.
The Black Cats suspended Johnson after he was arrested by Durham Police but the England international will now be allowed to train pending the outcome of the investigation.
"The club has discussed the current position in detail with both the Professional Footballers' Association and Adam's representatives," read a Sunderland statement.
"In line with those discussions we recognise that the player is entitled to re-commence his duties with the club while the legal process continues. He will therefore return to training.
"The club's own investigation cannot continue until the conclusion of the legal process. Sunderland AFC will make no further comment on the matter due to the ongoing police investigation."
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