The Tigers have been hard at work in pre-season for a while but without their members of England's touring party to South Africa.
The likes of Jonny May, George Ford and Ben Youngs have now returned although Ellis Genge remains on the sidelines after knee surgery.
Scotland back-row forward David Denton is also with his new club-mates after joining from Worcester and O'Connor has praised his men for coming back in great shape.
"It is good to have a full complement back so we can start planning in earnest," he told Leicestershire Live. "They are great pros. They looked after themselves in their five weeks off.
"It's really important they get a break from the game mentally as well as physically, so they have come back really excited about the season in front of us and making sure we are as good as we can be."