Twenty-seven year-old Sidoli was due to return in mid-January after undergoing an operation on his injured shoulder. However, according to Cardiff Blues coach, Dai Young, he is unlikely to make his return before the end of the month.
The 6ft 6 second row will be a great loss to the Wales line-out and with Ospreys lock Ian Evans ruled out for the rest of the season, Wales' options are limited.
Evans' Ospreys partner Alun Wyn-Jones looks most likely to claim the number five jersey, with Brent Cockbain and Ian Gough both vying for the other second row spot.
Back row Jon Thomas is recovering well, and is due to make his return to action two weeks ahead of schedule for the Ospreys.
Gareth Thomas is also returning to fitness after sustaining a knee injury in December.
Coach Gareth Jenkins will hope to have both players fit ready for Wales' opening match with Ireland on February 4.