American Johnson - an eight-time winner on the PGA tour - released a statement on Thursday announcing his intention to take a break from the game "to seek professional help for personal challenges I have faced", meaning he will miss next week's PGA Championship and the Ryder Cup at Gleneagles in September.
However, Johnson did not elaborate further and McGinley believes the 30-year-old should provide details to avoid speculation over his absence.
"Things will be said that are not true," McGinley said during a commentary stint for Sky Sports.
"It's much better for everyone if there is clarity. If something has gone wrong and he has been misbehaving, let's put it out on the table and get it dealt with and move forward."
United States Ryder Cup captain Tom Watson has wished Johnson well and is disappointed he will not be able to call on the player's talents for the biennial tournament.
"We will certainly miss Dustin Johnson at Gleneagles," Watson is quoted as saying by the PGA's official website.
"As one of the longest hitters in the game with an undefeated record of 3-0-0 at Medinah in 2012, he has clearly been an asset for the United States team.
"I am looking forward to teeing it up in the [US] PGA Championship at Valhalla, and finding out along with everyone else, which players qualify for the team based on points."