The England international will miss Friday night's clash against Sale Sharks at Edgeley Park after breaking a bone in his hand during the 21-15 victory over Bath last Saturday.
Scrum-half Matt Powell will take over as skipper, although Worcester are optimistic Sanderson will recover in time to face Newcastle on Friday week.
Worcester rugby director John Brain said: "Pat has broken a bone in his hand and he will be in plaster until early next week.
"He is out of the game tomorrow night, but he has a chance of featuring against Newcastle.
"It is not the ideal time to lose Pat, but Tom Harding will replace him in the team and he has had a good season.
"He is a real workaholic on the field, he gets through a lot of tackles and he is a skilful player.
"I am sure he will relish the opportunity to start such an important game."
Worcester hauled themselves back to within four points of 11-placed Northampton by beating Bath, although Saints still have a game in hand.
And the Warriors will travel to meet a Sale side boosted by the appearance of England pair Mark Cueto and Chris Jones, who were both released from Six Nations training duties earlier this week.
The struggling champions also hand a debut to full-back Julien Laharrague, who has joined from Perpignan, while fly-half Daniel Larrechea returns from suspension.
Sharks coach Kingsley Jones said: "It is tough at the moment, and while we have lost our last three games against Wasps, London Irish and Saracens, we have not been slaughtered, and I expect us to finish the season strongly."
Saracens hope to maintain their title play-off push by defeating Newcastle at Kingston Park on Friday, especially as the Falcons are without England trio Jonny Wilkinson, Mathew Tait and Toby Flood, plus injured full-back Matt Burke.
But Saracens rugby director Alan Gaffney said: "We will have a contest on our hands against a side that have inflicted a heavy defeat on Wasps two weeks ago, and we know we are going to be in for a very tough game.
"We have got six games remaining in the Premiership, and all of them are vital if we are going to maintain our push for a top four spot."