Exercising his right as a veteran, Uggla declined to go to the minor leagues after being designated for assignment by the San Francisco Giants in July.
He played in just four games for San Francisco, going hitless after being released by the Atlanta Braves after the All-Star break with a .162 batting average. The Braves still owe him $13 million for 2015.
The 34-year-old Uggla, who combined for 69 homers and 187 RBIs over the 2010-11 seasons for Florida and Atlanta, is batting just .194 since the start of the 2012 season. He has a career .243 average over nine seasons.
The 37-year-old Bell has 168 career saves. The three-time All-Star closer was released by Tampa Bay in May after he posted a 7.27 ERA in 13 appearances. He later signed a minor league deal with the New York Yankees.