The car he was travelling in with his two daughters is a write-off after colliding with a tram.
The accident happened in the Piazza Cinque Giornate area at around 8.30am.
Immobile, who was initially reported to have been unscathed in the crash, suffered "a distorsive trauma of the spinal column and a compound fracture of his eleventh right rib," a statement from Rome's Gemelli Hospital said.
He is otherwise in good condition, the emergency department of the top Roman hospital confirmed.
"The footballer remains in observation in the emergency department directed by Professor Francesco Franceschi of the Policlinico Universitario Agostino Gemelli IRCCS in Rome," the statement continued.
His daughters were not hurt in the crash.
Immobile said the accident was not his fault.
"The (tram) driver passed on a red light", he said.
Some 12 people in all were hurt in the crash, none seriously. Lazio has said Immobile may have to miss the next match. The side are currently second in on the Serie A table behind runaway leaders Napoli.
The fact that the 33-year-old footballer from Torre Annunziata near Naples, winner of the Golden Boot for top Serie A scorer four times, was not more seriously injured was apparently thanks to his air bag.
Immobile won the capocannoniere (top scorer) title at Torino in 2013 and at Lazio in 2016 and 2020.
The 2019-20 season was the most prolific of his career; he equalled the record for most Serie A goals in a season with 36, and won a third capocannoniere title and first European Golden Boot, given to the top scorer in Europe.
Immobile has also won an Italian Cup and two Italian Super Cup titles with Lazio.
He is at present Lazio's captain and the club’s all-time highest goal-scorer.
In 2022, he won the capocannoniere title for a fourth time, with 27 goals in 31 games.
By his standards, Immobile has had a poor season so far, managing only 12 goals, the last a penalty in Lazio's 3-0 win at Spezia on Friday, that consolidated their second place position in Serie A, 14 points behind runaway leaders Napoli.
Immobile has scored 15 goals in 55 appearances for Italy since 2014, but has been criticised for largely failing to find the net as Italy crashed out of World Cup qualification two straight times, for the 2018 and 2022 competitions.
ANSA
