Welsh coach Warren Gatland, whose side won this year's Six Nations, is making the "emergency dash" to ensure his son is "treated by a top medic", according to Wales Online.
The younger Gatland (23) will undergo major surgery to save his career after he was carried off during the Highlanders' massive win over the Sunwolves in Tokyo.
His foot was trapped under bodies, causing bones to snap and ligaments to tear. A surgeon reportedly believes he can reconstruct the foot so Gatland can resume his career, but his recovery period will be at least six months.
The injury is said to be worse than a similar one suffered by Wales back Jonathan Davies, who heard a few "pops and crunches" when tackled while playing Australia in late 2017.
Davies was out of action for nearly nine months, after having a plate inserted and enduring muscle wastage during the rehabilitation period.
Warren Gatland booked his flight home this week, just as he announced his initial Welsh World Cup squad.
Highlanders assistant coach Mark Hammett said Bryn Gatland had broken at least two metatarsals, damaged ligaments and displaced something else.
The horror injury has also robbed the Gatlands of a footy father and son reunion.
Warren Gatland is tipped to guide the Barbarians against Wales late this year. Bryn was in line to play for that team, giving his father the opportunity to coach him in a top side for the first time.
Gatland senior has also become favourite to coach the British and Irish Lions in South Africa in 2021, which would be his third successive tour with them.