The 19-year-old was due to stay at Kingsmeadow until mid-January.
Bees manager Uwe Rosler made the decision after his squad was hit by a host of injuries.
In midfield alone Rosler has recently lost Kevin O'Connor, Tom Adeyemi, Jonathan Douglas and Marcello Trotta to injury.
He said: "With injuries to experienced players, we are missing them."
Reeves, who played five games for AFC Wimbledon, will go straight into the Brentford squad for their Johnstone's Paint Trophy tie at Southend.