The club have confirmed that winger Cristian Montano was one of six players arrested as part of a National Crime Agency (NCA) investigation following claims by The Sun newspaper that a Championship game had been affected by fixing. He has subsequently been suspended without pay while the investigation is ongoing, the club said.
Blackburn striker DJ Campbell is also among those to be arrested, his club confirmed. Five of the six players have now been bailed until April 2014.
Asked about Montano's involvement, Johnson told Oldham's official club website, oldhamathletic.co.uk: "Anybody who saw that report will have been devastated and sick to their stomachs.
"However, we have to let the authorities do their job and duties, and we cannot prejudice that.
"The reason why I am in (the game) is because there are so many great people around the place and who are giving everything to the cause.
"There is a lot to celebrate about this club, and we have to make sure we don't forget that."
Johnson added the club will have to wait for the results of the investigation before they can determine Montano's future.
He added: "It is disappointing how somebody can get themselves into that situation.
"The truth is that we don't know yet what has happened for him to be in the room talking about that.
"I feel we have to step back and, as manager, it is my job to rally the troops and I am sure the players have that desire for three important games in the next 10 days."