"I want to put my skills and experience at the disposal of the club at a key point in the season, while at the same time making progress in my physical condition and getting into the rhythm of competition," Gasol wrote.
"I'm happy to return to the club where I began, and I'm excited about this new opportunity: I hope to contribute to the first team very soon."
Gasol is coming off a challenging rehab process after having surgery late in 2019 to address a stress fracture in his left foot. The 40-year-old veteran attempted to make an NBA comeback with the Portland Trail Blazers, but the team subsequently waived him.
The Spaniard last played an NBA game in March 2019 with the Milwaukee Bucks.
After playing for Barcelona as a teenager, Gasol put together a Hall of Fame-worthy resume, averaging 17 points, 9.2 rebounds, and 1.6 blocks in 18 NBA seasons. He also earned six All-Star appearances and four All-NBA selections during his career.