Both players missed the FA Cup third-round defeat to Leicester last weekend. Diamond has not played since the league loss at Barnet on December 21 because of a virus while a hamstring injury ruled out O'Connor at the King Power Stadium.
"We could have risked Zander against Leicester but we decided he wouldn't be able to do himself or the team justice," said Burton boss Gary Rowett.
"He's feeling a lot better in himself now and hopefully he'll be able to train towards the end of the week to put himself in contention for the Torquay game.
"It's a bit early to say whether Anthony will be back but he's progressing really well in terms of his recovery."
Rowett is also optimistic that leading goalscorer Calvin Zola will shake off a groin problem.
He added: "Calvin always suffers a bit when he plays a lot of football in a short space of time. But with us not having a midweek game he's had time to recover and he should be okay by the weekend."