That kept him out of the summer tour to Australia, in which Wales lost all three Test matches by narrow margins.
But with Argentina , Samoa, New Zealand and Australia all coming to the Millennium Stadium this autumn, the 25-year-old Roberts will be desperate to return to full fitness.
And Davies, who only arrived at the Blues over the summer, admits he has been taken by surprise at how quickly Roberts is getting back to fitness.
He said: "I have been really impressed with Jamie. He's been back in since day one and is working especially hard.
"Jamie has been outstanding and will, hopefully, be back playing sooner or later.
"We don't know when it's going to be for certain, whether it will be September or October.
"But Jamie has been setting an excellent standard and he will be ready to play for the Blues before the autumn international campaign."