England captain Peacock has won 26 caps for Great Britain
Leeds prop Jamie Peacock is facing up to another four months on the sidelines after surgery for knee ligament damage.
There were slim hopes that the England captain, who has been out since August, could return in February.
But Rhinos head coach Brian McDermott said: "JP and Danny McGuire are working hard to get back to fitness.
"We have always known that we would start the season without them but it will give us a great boost when they come back in mid-season."
Stand-off McGuire suffered a knee injury during Leeds' 27-26 win over Wigan in last year's play-offs - and was always expected to miss the start of the new season.
Peacock picked up the injury against Castleford in August and went under the surgeon's knife in September, missing the Challenge Cup final, the play-offs and England's Four Nations trip down under.
They are in the best possible hands with our medical team
Rhinos coach Brian McDermott
And both have had to watch from the the sidelines since the Rhinos squad returned for pre-season training in November under their new head coach.
"It is hard to say with those guys that they are on schedule because it is such a long-term injury, but they are over halfway now with their rehabilitation.
"That has certainly lifted their mood. As with any long term injury, you have good days and bad days but they are in the best possible hands with our medical team and they are putting in the hard work required.
"We are looking forward to having them back on board."