The 22-year-old international garnered worldwide attention following last year's Club World Cup, but appears set to join the Japanese-friendly Bundesliga this summer
The Japan international has long been rumoured to make such a move this summer following this summer's London Olympics.
But after clubs ranging from German champions Borussia Dortmund to Portugal's Porto expressed interest in the 22-year-old, Hannover have proven to be the most enthusiastic.
"We have to consider what [Sakai] himself wants and finalise the terms of the contract," Reysol general director Yukitaka Omi told the paper.
"We also can't come to an agreement without deciding on the transfer fee."
Hannover have reportedly offered the reigning J-League champions €1 million for the star right-back, who would be signed to a four-year contract.
A pillar of Japan's Olympic hopes, Sakai has scored one goal in seven league appearances for Reysol in addition to two goals in five Asian Champions League matches so far this season.
"It should be announced when everything is officially decided," the player told Hochi. "I've known what I want to do for a long time, but whether I stay or leave [for Hannover] it has to come to a conclusion soon."