Allen, 21, could now make his debut for Dave Hockaday's men in the New Year's Day trip to Aggborough against Kidderminster Harriers.
"Chris has been a ever present with Marine during their successful year to date, including their fantastic run in the FA Cup," said a club statement.
Allen's arrival comes just a day after Forest Green confirmed that former club captain Mike Fowler, along with defender Curtis McDonald, is leaving Rovers to join Blue Square Bet Premier rivals Newport County.
Source: BBC Sport
Source: BBC Sport