The midfielder who can also play at wing-back is wanted by Antonio Conte as he looks to add depth to his squad ahead of the new season.
The Italian is known to be frustrated with Chelsea’s business this summer.
But Roberto could be the man to solve some of his problems, according to the bookies.
BetStars Director of Trading Ian Marmion explained: “Chelsea have identified Barcelona’s Sergi Roberto as their top transfer target this summer as they look to add depth to their squad before the transfer window closes.
“The 25-year-old Spaniard is high on Antonio Conte’s transfer wish list and his versatility to operate as a midfielder and wing-back will no doubt appeal to the Blues manager who wants to strengthen in both positions.
“The Spanish international, who was used primarily as a wing-back at the Nou Camp last season, could be enticed by the prospect of a starting spot in his preferred position as a holding midfielder at Stamford Bridge this season and is priced at 8/11 to make the swap.”
Chelsea have so far added four new players to their ranks as they prepare for a return to the Champions League.
Antonio Rudiger, Willy Caballero, Tiemoue Bakayoko and Alvaro Morata have all made the switch to Stamford Bridge.
But Nemanja Matic has left for Manchester United with Diego Costa also expected to exit the champions.
Chelsea start their Premier League campaign on Saturday when they take on Burnley at 3pm.