The Ireland starting line-up for the clash with the Cherry Blossoms will be confirmed tomorrow morning (Wednesday) at 9.00am Irish time, following a training stint at the Kintetsu Hanazonon Stadium.
O'Donovan, who informed Simon Easterby of his Lions call-up before take-off on Saturday at Shannon airport, will have a full compliment of 26 players to pick from.
Although Japan (17th) are ranked ten places below Ireland in the IRB World rankings and lost 100-8 against Scotland last November, O'Donovan is expecting a tough examination.
"Although they lost to Canada in the recent Super Cup final, Japan still showed enough form to make them a threat this weekend," explained the Shannon man, who along with Declan Kidney, helped Munster to the 2000 and 2002 Heineken Cup finals.
"Their ability to play to the hard and fast conditions makes them dangerous in broken field play, but equally I feel we will also be looking to play to the conditions. Any team that
The Irish players have already been given a taste of the local temperatures and dry conditions, having trained on both Monday and Tuesday in 30+ degrees, and on bone-dry training pitches.
O'Donovan, who is likely to confirm a couple of international debuts tomorrow, added: "Sunday's first Test will offer the players in the squad a chance to lay down a marker with their performance for next season and the Autumninternationals ahead in November."
The Irish squad, which contains eight uncapped players, lines out at Osaka's Nagai Stadium at the weekend. The Japanese Union are expecting between 25,000-30,000 locals, with 200 Irish supporters in their midst, at the 55,000-capacity venue.