Second-row Thorn also needs dispensation from the IRFU to join Joe Schmidt's ranks as Leinster bid to retain their Heineken Cup crown and end their recent wait for the RaboDirect PRO12 title.
"He has won most trophies in rugby but nothing in the Northern Hemisphere yet, that is something that might interest him," said Schmidt.
"Brad is pretty keen to come if it's possible. That's the first step. The second step is gaining approval from the IRFU and they have been very good. They can identify the problem themselves that we do have a real shortage in the second-row.
"That would be something they would agreeable to, as long as we can get the agreement from the Japanese club. We are waiting for some feedback from them.
"We would need him by March to get a three-month contract that covers us for the ERC games as well as the Rabo games."
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