Roberts played on for more than a quarter-of-an-hour before being rushed to hospital.
His contribution during his short time on the pitch was critical to the outcome of the match as he set up the final ruck prior to Shane William's opening try. The 22-year-old medical student picked a superb supporting angle to take play to within 10 metres of the Wallaby tryline after Williams and Lee Byrne had combined in midfield.
"Jamie has sent us a text from hospital telling us he has a fractured skull," said Wales and Lions coach Rob Howley.
"That just sums up the team spirit - a guy is in hospital but sends a text message to the players who he has been playing with for the past three weeks.
"I think that is a testimony to the squad and the team spirit that Warren has achieved over the last three weeks."
"It was a hell of a collision but he bravely carried on," added Wales captain and 2005 Lion Ryan Jones.
"He's put his heart and soul into the jersey and you can't ask for any more than he has given."
Roberts will miss his region's back-to-back Heineken Cup clashes with Biarritz next week and the week after but could possibly return for the final two European group matches taking place in mid and late January.