Police in Tottori prefecture, southwest Japan, where the incident occurred in late October, recommended that Mongolian-born Harumafuji, 33, be charged, NHK public TV and Kyodo news agency reported. Tottori police could not immediately comment on the reports.
The former "yokozuna", or grand champion, retired and apologised last month for injuring junior wrestler Takanoiwa while drinking at a restaurant-bar with other wrestlers.
A report by the Japan Sumo Association's crisis management committee found that Harumafuji, angered that Takanoiwa was checking his smart phone after being chastised for a bad attitude by fellow Mongolian "yokozuna" Hakuho, slapped and hit the younger wrestler with a remote control device.
Harumafuji told a news conference announcing his retirement that he felt it was his duty as a senior wrestler to correct his juniors when they were rude, but conceded that he had gone too far.
Takanoiwa did not take part in the latest tournament due to his injuries, which the sumo association had previously said included a fractured skull and concussion.
The incident has highlighted sumo's struggle to reform harsh conditions that can breed violence in its closed, hierarchical world, although some wrestlers say there have been improvements in the decade since a trainee was beaten to death.
Harumafuj's lawyers later on Monday released a statement on behalf of the former grand champion, offering "heartfelt apologies to Takanoiwa and others," Kyodo said, without identifying the lawyers by name.
The lawyers said they would seek a meeting with Takanoiwa and his "stablemaster", or coach, Takanohana, to apologise and discuss compensation, Kyodo added.
(Reporting by Linda Sieg, editing by Nick Mulvenney)
