Vunipola had not featured for Sarries since suffering a knee injury in September and was reportedly in danger of missing the start of the Six Nations next month.
His return in Sunday's impressive victory put any doubts about his participation with England to bed as he produced a trademark all-action display at the Ricoh Arena.
And that was a joy to behold for McCall, who also welcomed back Maro Itoje from a broken jaw.
"I thought he [Vunipola] was great," the club's director of rugby told BT Sport.
"It's actually extraordinary to play that well when you’ve not played all season so he'll be all the better for that."
— Saracens Rugby Club (@Saracens) January 7, 2018
Sarries forward coach Alex Sanderson also praised the returning number eight, describing Vunipola as a "force of nature".
"We could've played him last week, but didn't want to put him out there too early," he said.
"But we're fully away that Billy being the force of natural, the athlete he is, still has the natural ability to bump people off, break tackles, to create something from nothing.
"In today's game that has been dominated by defences in recent years you need players like that to get on the front foot."
Photo Getty Images. Caption: Saracens forward Billy Vunipola