World Cup winner Toni, who joined Genoa at the start of the season after AS Roma opted not to make his loan move from Bayern Munich permanent, signed a deal until June 2012 after arriving on a free transfer.
"You can never say no to Juve," Toni told a news conference. "I've realised a dream and I am extremely happy. When the transfer was proposed to me I didn't hesitate and I didn't have any problems reducing my wages."
In-form Italy forward Quagliarella suffered the injury after three minutes of Thursday's 4-1 home defeat by Parma and a new striker in the transfer window became a necessity for Juve given Vincenzo Iaquinta is also out with a thigh problem.
"In the coming days Quagliarella will undergo reconstructive surgery on the ligament. The prognosis is around six months," Juve said in a statement.
The Turin club, hit by a string of injuries in recent years, had been linked in the media with Fiorentina striker Alberto Gilardino and Catania's Maxi Lopez even before Quagliarella's injury but have taken Toni despite his poor form.
Toni, 33, has scored only three times in the league for Genoa this season and has not featured for Italy in two years.
ANOTHER STRIKER
Local reports say Luigi Del Neri's side may try to sign another striker later in January.
Juve, who also have the ageing Alessandro Del Piero and inconsistent Amauri for up front, were hoping to mount an assault on the Serie A title in the second half of the season but lie eight points behind leaders AC Milan after Thursday's defeat.
Quagliarella is on loan from Napoli with a permanent deal planned for the end of the season, which could now be in doubt.
On a bad day for Juve following Thursday's thumping, Felipe Melo was banned for three matches after being sent off against Parma for kicking out at Massimo Paci while goalkeeper Marco Storari had checks on a chest injury.
Gianluigi Buffon is back in full training for the first time since injuring his back at the World Cup so could come in for Storari at Napoli on Sunday.
Del Neri had initially said Buffon, whose future at Juve has come under scrutiny given Storari's good form, would return next Thursday in the Italian Cup last-16 game with Catania.
