Jenas, 29, came through the youth ranks at the City Ground and scored four goals in 33 games before he was sold to Newcastle for £3.5 million as a teenager in 2002. He moved on to Tottenham in 2005.
Talks had been held over a return to the banks of the River Trent in the summer but they fell through. However, revived discussions have seen Forest fend off interest from other clubs to land the former England international.
Forest announced: "Nottingham Forest can confirm Jermaine Jenas is to return to the club on an emergency loan from Tottenham Hotspur."
Jenas, who was named in Tottenham's 25-man Premier League squad last month, has been a peripheral figure at White Hart Lane in recent years, with fitness problems meaning he last started a match for Spurs in April 2011.
A loan spell at Aston Villa was cut short last year after he suffered a season-ending Achilles injury. Jenas is expected to go straight into the Forest squad for the televised clash against local rivals Derby at the City Ground on Sunday afternoon.