Richards has been sidelined since February after he sustained a knee ligament injury that required surgery.
The England international has been steadily working his way back to full fitness, and head physiotherapist Ally Beattie has confirmed Richards is now over the injury.
"Micah has been working hard with us after the season finished, and he's at the stage now where if the season was still on now he'd be able to fully train and probably play. He'll be ready for pre-season," Beattie told the club's official website.
Onuoha, meanwhile, has been out of action since April after dislocating his shoulder against Chelsea.
Beattie added: "Having dislocated his shoulder, Nedum was never going to be fit again before the end of the season but he's made excellent progress with his rehab and he'll also be ready for pre-season."