Parker links up with former R's manager Gary Waddock and will be playing his football at Adams Park until February 26.
The 19-year-old is in line to make his Wycombe debut against Torquay on Tuesday and Neil Warnock feels the move will help Parker earn some valuable first-team experience.
"Josh needs games - and the more the merrier at this stage of his career," he told the club's official website.
"I think he's got a great future, but he needs to gain experience and he'll get that at Wycombe."
Source: PA
Source: PA