Greenwood, sidelined since December after undergoing shoulder surgery, kicked two penalties as Harlequins reserves beat Bath United 6-3 on Tuesday night.
Greenwood, who featured at fly-half, landed his match-winning penalty four minutes from time and could now be in contention for Quins' Zurich Premiership clash against London Irish on Saturday week.
The Irish encounter is just two days before Sir Clive Woodward announces the British & Irish Lions squad for this summer's New Zealand tour.
Greenwood, capped 55 times by England, toured South Africa and Australia with the Lions in 1997 and 2001, respectively, and he has an outside chance of making a third trip.
He is not alone in needing to prove his fitness to Woodward, as England World Cup-winning colleagues Jonny Wilkinson, Richard Hill, Mike Tindall and Phil Vickery are all currently fighting injuries.