The 27-year-old midfielder was suspended by the Black Cats earlier this month following his arrest on suspicion of sexual activity with a girl under 16, but will now be free to resume while the police investigation continues.
A club statement said: "The club has discussed the current position in detail with both the PFA (Professional Footballers' Association) and Adam's representatives.
"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."
Source : PA
Source: PA