The Professional Footballers' Association was "as shocked as anybody" when Adam Johnson pleaded guilty to grooming and kissing a 15-year-old girl, chief executive Gordon Taylor has said.
Mr Taylor told ITV News that the PFA did not put any pressure on Sunderland to reinstate Johnson following his suspension when he was first arrested in March last year.
He said the organisation was not present at a meeting between Johnson, his barrister and the club and was not told any details about the evidence.
Mr Taylor said: "We were as shocked as anybody on the first day of the trial when he pleaded guilty to two charges."
The PFA chief executive said Sunderland had taken independent legal advice and acted in accordance with Johnson's contract.
Mr Taylor said: "At the time of his arrest in March, then he was one of our members so we should know what was happening and Sunderland kept us informed that he was being suspended for 14 days in accordance with the contract.
"As one of our members of course we were interested to know what they were doing, they kept us informed and then, at the end of that suspension, he'd been arrested but there were no charges and, as a result, they told us he was being reinstated into the club."
He added: "It would be their choice whether he played or not."
When asked if the PFA knew that Johnson had admitted kissing his victim, Mr Taylor said: "Why would we know if we didn't get told?"
In a statement last week, the PFA said it had "much work to do" in educating players about standards of conduct and described the case as "extremely disappointing".