The powerful back-row forward returned from a fractured forearm suffered in January to feature in the 51-14 victory over London Irish on Sunday.
There were fears the 25-year-old had swiftly fallen victim to yet another fitness setback after he experienced an issue on Wednesday.
And while Vunipola is indeed set to miss Saturday's regular-season Premiership finale against Gloucester, Saracens' director of rugby McCall claimed his star should be back for the team's subsequent last-four showdown against Newcastle Falcons or Wasps.
"[The hamstring] hasn't been pulled or anything, as far as I know," McCall was quoted as saying by the BBC.
"There are two and a half weeks until the semi-final, so all things considered it's probably best he doesn't play this weekend.
"If anyone has a hamstring tightness on Wednesday, it wouldn't be the most sensible thing to play him [on Saturday].
"Maybe having not played rugby for a long time, these kind of things can happen quite easily."
After Vunipola missed the Six Nations, England coach Eddie Jones will hope to have him back for three Tests away to South Africa in June.
Photo Getty Images. Caption: Billy Vunipola of Saracens