Saracens, last season's losing Premiership finalists, want the double Grand Slam winner to fill in for injured fly-half Derick Hougaard, who is set to miss the rest of the season with an Achillestendoninjury.
The 35-year-old's injury problems were sparked by a sprain of his knee and a strain of his Achillestendon during the third round of the Masters in April.