Trio set to return for Millers
And, says manager Steve Evans, the Millers are looking forward to testing themselves against the League One leaders.
The influence of Arnason, O'Connor and Frecklingon was missed in Tuesday's frustrating home draw with Tranmere Rovers.
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Hide AdBut with Arnason now recovered from illness and O'Connor and Frecklington back from suspension, Evans will be able to field something like his full-strength side in the quest to end a run of three matches without a league win.
He told the Advertiser: "Arnason, O'Connor and Frecklington are big-game players and it is good to have them back available for a game like this.
"We're facing an Orient squad that's been together for 15 or 16 months and just missed out on the play-offs last season. It doesn't get any tougher than going to play the leaders but we've nothing to fear.
"We have to play through this spell and believe that if we keep the standards up then the rewards will come."
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Hide AdEvans dropped Alex Revell on Tuesday and has to decide whether to recall the striker.
Meanwhile goalkeeper Adam Collin, who was handed his first league start in place of Scott Shearer, will be hoping to be included again.