The lively winger was a fans' favourite at Allianz Park, but Sarries' director of rugby McCall fears he could return to haunt them in Saturday's showdown as the English side seek a second consecutive Premiership and European double.
With 11 tries in 15 games, Strettle is likely to be Clermont's danger man at Murrayfield and McCall knows it.
"Strettle is playing outstandingly well at the moment, he was playing outstandingly well when he left here," he said of the 33-year-old, who departed in 2015.