The yen is likely to reach its strongest level against the dollar in more than six years if Japan enters a recession, which could come as early as the fall of this year, a former central bank official has said.

"I don't think it will hit the 70s, but the 80s is quite likely," said Hideo Hayakawa, former chief economist at the Bank of Japan, in an interview on Tuesday.

The BOJ would be powerless to stop such a move, though it could slow it down by introducing a negative lending rate, one of the few policy options it has left, said Hayakawa, a consistent critic of the BOJ's current stimulus policies.