The British Lions wing has not played since returning from New Zealand with a similar problem to the one that has ruled out team-mate Gavin Henson until mid-October. Now he is targeting a similar comeback date as he battles to prove his fitness for Wales's opening game of the Autumn Series, against the All Blacks in Cardiff on November 5.
Ospreys assistant coach Sean Holley said: "It is a worry because Shane just hasn't been able to shake off the problem but it is still our hope that he will be fit for the Heineken Cup and then for Wales in the Autumn."
Williams is the sixth member of Mike Ruddock's squad to be sidelined by a groin problem.
Nearly 40 players were involved in the first Wales Under 18 training session of the season. WRU National Performance Manager Gethin Watts is excited at the potential shown by the group and expects the Regional Under 18 Championship to hone their skills even further.