The England international is no stranger to injuries, as he only made his return from three months on the sidelines with a broken arm during Sarries' 51-14 victory at London Irish on Sunday.
Indeed, the 25-year-old has played only 249 minutes of competitive rugby over the last year due to shoulder, knee and arm injuries, so concerns were raised when he pulled out of a Saracens training session on Wednesday due to a hamstring issue.
However, Sarries' director of rugby Mark McCall is hopeful the injury is not too serious and he has praised Vunipola for the maturity he showed in recognising the problem before it became anything too serious.
"Nothing happened, he just felt some tightness and awareness of that tightness. The hamstring hasn't pulled or anything," McCall said. "It was mature of him not to try to plough on in training. If we have to scan it we will. That's likely to happen, I would have thought."
Saracens are already assured of a second-place finish in the Aviva Premiership as well as a home semi-final in the play-offs, so Vunipola may not be risked for this weekend's clash with Gloucester at Allianz Park.
Vunipola's latest injury scare will have also concerned England coach Eddie Jones, who is set to name his squad for the upcoming three-Test series against South Africa next Thursday.