Kubica was taken to a local hospital for X-rays on his right leg after the fall in Pietrasanta, northern Italy.
Unconfirmed reports suggest Kubica has aggravated the right-tibia fracture he suffered in a high-speed rallying accident last February.
ANSA's report said that Kubica later left the local hospital in order to receive treatment at the Pietra Ligure hospital, whose specialists have overseen his recovery following last year's accident.
The Pole missed the whole of the 2011 season as he recovered from his injuries - which included a partially severed right hand - while his Lotus Renault team have also ruled him out of the start of the 2012 season, electing instead to name Kimi Raikkonen and Romain Grosjean as their drivers.
Kubica's camp have nevertheless maintained his goal of returning to F1 remains unaltered, with Ferrari widely believed to be monitoring his fitness ahead of a potential drive in 2013.
ANSA, quoting sources at the local Versilia hospital where Kubica was initially treated, later reported that he had suffered a "microfracture" to his right ankle.
Doctors applied a splint to the injury before his relocation to the Pietra Ligure hospital.