The 22-year-old has now been farmed out to the Biancocelesti after returning from a short spell at Vitesse Arnhem earlier this month
The 22-year-old has joined the Roman club for a fifth loan stint away from Stamford Bridge, having previously enjoyed spells with Fulham, Bolton Wanderers, Dijon and Vitesse Arnhem after becoming a Blues player in 2007.
The midfielder was banned for four months in 2009 after being found by Fifa to have breached his contract with Lens when signing for the London club, but has since managed just 16 games in all competitions for Chelsea.
He will now join a Lazio midfield shorn of the services of Anderson Hernanes, who has signed for Inter in a €20 million transfer, having been recalled from his second season-long loan at Vitesse at the beginning of January.
The Frenchman, who has been capped at every level from under-16 to under-21, has played a total of 69 games in his combined loan spells and scored 11 goals, with three of them coming in 14 games for Vitesse this term.