Osmajic had until Monday to respond to the charge and Ridsdale told talkSPORT on Tuesday that the player had “responded within the time frame”.
Ridsdale added: “He has accepted the charge that the FA put to him which was that he was seen to bite the opposing player in the game against Blackburn Rovers.
“We’ve already indicated to the player what we’re doing. I want to keep that obviously in-house but you can be assured that that’s not something that we condone as a football club and we’ve taken appropriate action.”
Both the FA and Preston declined to comment when approached by the BBC.
Blackburn manager John Eustace told BBC Radio Lancashire following the game: “Owen’s got a big bite mark on the back of his neck and it’s a shame the referee didn’t see that.”
Luis Suarez, then of Liverpool, received a 10-match ban in 2013 for biting Chelsea’s Branislav Ivanovic.