Howell developed a blister on his foot that required aggressive treatment to prevent infection and possible amputation.
"Because of bad circulation, something like that can be a real problem for me," Howell said on Thursday. "But everything's back to normal."
Until Howell left the club, the bullpen ERA was 2.84. In his absence, it was 3.13.
"The biggest thing is for the guys to get themselves in position and defined roles so Donnie [Mattingly] can know when to use them," said Howell. "Players have to make that happen with performance."
Jim Slaton, who filled in for Howell, returned to his role as pitching coordinator at Camelback Ranch-Glendale.