The 23-year-old arrives with the U's leading goalscorers Jabo Ibehre and Freddie Sears currently sidelined by suspension and injury respectively.
Hewitt has made one substitute appearance for QPR to date and spent a brief spell on loan at Dagenham last season, although his most first-team experience has come this term having made 12 appearances for League One rivals Bury, during which he found the net twice.
The striker is available to make his debut in Saturday's home clash against Crewe.
- Sports & Recreation
- Freddie Sears
- Jabo Ibehre