The Daily Telegraph said the 28-year-old defender was ordered to train with the club's development squad after manager Terry Connor was made aware that he was under the influence of alcohol.
Johnson, who was fined two weeks wages following the incident, issued a short statement apologising for his behaviour.
"My conduct and approach to training on Monday was below the high standard the club rightly needs and demands of me, and what I demand of myself," he said.
"As a result, I have apologised to the manager, my team-mates and the club."
The incident occurred on Monday, with several of Johnson's team-mates remonstrating with him over his condition.
Interim manager Connor said Johnson had "apologised and accepted punishment" for a "breach of club discipline."
"The matter has been resolved internally and the club will be making no further comment," he said.
Johnson joined Wolves from Birmingham last summer but has been unable to prevent a poor campaign which has left the club languishing third from bottom.
Source: AFP
Source: AFP