كتب : Omar AbdelAziz
The 23-year-old left the Malian camp for two days in order to sign with the Old Lady, before heading back to Ghana to face Ivory Coast in the African Cup of Nations.
Sissoko, who played under the management of Claudio Ranieri with Valencia in 2004, expressed his delight by reuniting with his former coach.
"I am happy to come to such an important club, this experience is certainly a step forward in my career," Sissoko said in a statement.
"I am excited at the thought of soon being able to play with great champions and to work again with Claudio Ranieri, a great coach who I already appreciated during my time at Valencia."
Sissoko's arrival in Turin follows the signing of Lazio defender Guglielmo Stendardo on loan, as well as reaching an agreement to sign Aston Villa's Olof Mellberg on a free next summer.