Centre-back Williams is to face at least six weeks on the sidelines with an ankle problem while Okenabirhie and John are expected to be out for around another four and three months respectively.
Okenabirhie has yet to play a game this season because of injury but manager Richie Wellens hopes he will be able to play some part for Rovers before the end of the campaign.
John made six appearances for Doncaster in August but has not played since fracturing his back in the League Cup against Stoke City.
The news that he will be out for a further three months comes as a blow for Rovers however, having a timescale on his return provides a little encouragement after he was initially ruled out indefinitely.
“Fejiri is going to be out for another four months,” confirmed Wellens.
“I think he was probably mis-treated at the start of his rehab, around February or March time.
“I don’t want to go into too much detail about it but he’ll be four months. As long as we keep his fitness up, which we will, he may be available for the last nine or ten games but he’s been out a long time.
“And Cameron John is going to be another three months. He’s more or less got the same injury what he had three months ago.”
Williams picked up his ankle problem against Crewe Alexandra. He would have been suspended for tomorrow's fixture against Lincoln City regardless but is unlikely to play again before the end of the year.
Wellens added: “He damaged his ankle against Crewe. We had the first cup game against Scunthorpe and he was sore but decided he wanted to be on the bench.
“We knew it was too early to put him on when Joe Olowu went down injured. We had it scanned the next day and he’s out for six weeks.”
Olowu has been passed fit to face Lincoln, along with John Bostock but the fixture will come too soon for Ben Close who will miss the game with a hamstring issue.
Dan Gardner and Jordy Hiwula will not be involved but on a more positive note for Doncaster and Wellens, Jon Taylor is likely to be fit after recovering from an ankle problem.
“It’s great news, he’s trained all week, he’s more or less pain free," said Wellens of the midfielder who has been struggling with the injury since March.
“He’s got an appointment with the surgeon next week which should relieve all the pain. Next Wednesday he should be 100 per cent pain free.
“He’s trained comfortably enough this week through the pain barrier to allow him to be involved this weekend. He does everything at 100 miles per hour. With the ground he covers, he does a lot of it at high intensity.
“He’s not a player you can hold back, he’s an experienced player so you can trust him with his body more.”