His Irish side got off to a flying start in Edinburgh last weekend, recording their first win at Murrayfield since 1985 with a 36-6 win over Scotland.
The victory came at a cost however, and with another game against Italy in Rome just six days later O'Sullivan said: "We have a lot of tired bodies from last weekend. Even now the lads are still pretty beaten up and we've had another travel day, so it is a concern."
"I think the Italians are sitting there waiting for us with an extra day's recovery and no travel day in their week. But that's part of life now and we have to cut our cloth accordingly."
O'Sullivan is expecting another bruising encounter with the improving Italians, who he believes have added structure to their strength under coach John Kirwan.
He said: "It's a very different Italian team these days. They've retained their strength in the set-pieces that Brad Johnstone brought but now John Kirwan has added a few strings to their bow."