The Ladbrokes Premiership leaders began their winter training camp yesterday and will train twice a day over the next week to keep themselves fit before returning to action with a Scottish Cup clash against Brechin City on January 20th.
Roberts did not join in with the rest of his team-mates, as reported by the Daily Express. Instead, he continued to work with the physios as he looks to overcome the hamstring injury which has kept him out since late November.
The Manchester City loanee sustained the injury in his comeback match from a previous hamstring problem, and the club are being understandable cautious with the player.
Celtic hope to have him back in time for the first leg of their round of 32 clash with Zenit St Petersburg in the Europa League on 15 February.