Townsend suffered the injury in the 73rd minute and was immediately substituted, and Sherwood, who replaced the sacked Andre Villas-Boas on Monday, fears the 22-year-old England international could be ruled out for some time.
"It looks like it," he was reported as saying by the BBC. "It looks like he pulled up with a hamstring."
Townsend has made 14 league appearances for Spurs this season, having spent last term on loan at Queens Park Rangers, and made a spectacular start to his England career, scoring on debut in a World Cup qualifier against Montenegro in October.
Tottenham, who dismissed Villas-Boas following a series of poor results despite heavy investment on players, next play Southampton in a Premier League clash on Sunday.