But he is targetting an ahead of schedule return to hand both the Ospreys and Wales a major boost.
Williams is hoping to be available for his region's final game of the season against Aironi on May 6, ahead of Wales' World Cup warm-up matches.
"I started running this week again and the knee feels great," said Williams.
"I don't want to push it and make it worse but I'm aiming for the Aironi game."
A rest period of six to eight was the original diagnosis after Williams damaged his posterior cruciate ligament against Ireland on March 12.
That ruled Wales' record try-scorer out of the Ospreys push to defend their Magners League crown.
The reigning champions have lost twice and drawn once since the Six Nations to leave their chances of reaching the Magners League play-offs hanging by a thread.
Victories in their final two games, at home to Munster and then away to Aironi, might not be enough, with the Ospreys dependant on other results.
But the return of Williams for the final league clash in Italy would be a huge boost.
"We know Munster are a very good side," added Williams.
"They are very experienced and have been there or thereabouts for a number of years now.
"But we've certainly got the players and strength to beat them and it's a great game for us to go out and win.
"It'll give us confidence and hopefully we can go to Aironi and win that game as well."