With Jon-Paul Pittman out for 12 weeks with a dislocated shoulder and Deane Smalley still recovering from a groin injury ahead of four games in 11 days over the Christmas period, James Constable and Tom Craddock were the only experienced strikers at the club.
But now Antigua international Parker joins youngster Tyrone Marsh in providing manager Chris Wilder with more options.
"Josh has done well in training and now he gets a chance to show us what he can do over a slightly longer period," Wilder told the club's official website.
"Deane Smalley and JP Pittman are both out so we needed cover over the busy Christmas period and Josh is hungry to come in and impress."
Parker started his career at QPR, making five senior appearances for the Hoops before a permanent switch to Oldham for the start of the 2011/12 season. He played in 15 matches for the Latics.
The 22-year-old, who can play on either flank or in the middle of the front line, is expected to go straight into the squad for Saturday's npower League Two fixture against Fleetwood.