But, Webb is in line to feature when seventh-placed Ospreys travel to sixth-placed Munster on Sunday.
And Rees says Webb is ready to come back firing on all cylinders.
"He has been raring to go for a couple of months," said Rees.
"You have to go through the medical process and that can be hard at first, but Rhys takes all the potential stumbling blocks in his stride.
"We have good options at scrum-half. Brendan Leonard skippered the side for the last game and did well around the group, providing the leadership and key messages.
"But Rhys is champing at the bit and we want to get his qualities onto the field.
"There's a probability he'll be in the 23."
Meanwhile Ospreys have been assured that the ankle injury suffered by fly-half Dan Biggar at the weekend should not be cause for concern.
The 26-year-old left the field in the first half of Wales' draw with Ireland on Sunday, but the Welsh Rugby Union said: "Dan Biggar has made excellent progress with his ankle injury. Indications are it is not considered long-term."
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