In a massive lift for the Six Nations champions, the bulldozing number eight is poised to be included in the matchday squad for the Aviva Premiership trip to Newcastle.
If he proves his fitness, Vunipola is sure to come under serious consideration for Scotland's visit to Twickenham on Saturday week, providing the ball-carrying threat England have sorely missed in his absence.
The 24-year-old was expected to sit out the entire Six Nations because of the ligament damage sustained against Argentina during the autumn until Eddie Jones raised the prospect of him returning for the potential title decider against Ireland on March 18.
Nearly two weeks ago Vunipola ruled himself out of the remainder of the tournament, before Jones renewed hope of his return last Friday.
"It's pretty positive. We're working with Saracens to see when he's going to be available to play. We haven't written off him playing in the Six Nations. He's looking fit," Jones said.
Nathan Hughes has been deputising in Vunipola's absence but the Fijian-born Wasp rookie has had an underwhelming Six Nations to date, albeit while filling the boots of a back row colossus and world player of the year nominee.
Vunipola served as a rallying point for Jones' England until damaging his knee in the first half against Argentina, his ability to generate momentum from a standing start a key factor behind the team's success.
The game is well stocked with outstanding number eights - Kieran Read, Louis Picamoles, Sergio Parisse and Taulupe Faletau among them - but under Jones Vunipola has developed into a player of at least equal calibre.
His return would follow hot on the heels of his elder brother's comeback from his own knee injury as a replacement in the 36-15 victory over Italy, raising the prospect of both Vunipolas being unleashed off the bench against Scotland.
Billy and Mako and have acted as the main source of English momentum and may start in tandem for the climax of the Six Nations in Dublin, where a title, consecutive Grand Slam and 19th successive victory could be at stake.
Mako will start against Newcastle on Sunday in order to gain further match fitness.