Cox also gave a projected timetable for the returns of two more injured Braves pitchers, Mike Gonzalez and Rafael Soriano .
"I think within the next 12 days all three of them will be up here -- or close," Cox said.
Smoltz, 41, has been on the disabled list since April 29 with a sore right shoulder.
He said he was still dealing with inflammation and discomfort after his two bullpen sessions last week but had better success on Tuesday.
Cox hinted Smoltz may not need another side session in Atlanta before beginning a minor league rehabilitation stint.
"I don't know for sure," Cox said. "He felt awfully good yesterday."
Smoltz is 3-2 with a 2.00 ERA in five starts. He began the season on the disabled list with the sore shoulder and has been out more than three weeks on his second DL stint.
Smoltz plans to pitch out of the bullpen, probably as the team's closer, when he returns. He said pitching in relief should cause less stress to the shoulder.
Gonzalez, a left-handed reliever, is returning from Tommy John elbow ligament-replacement surgery.
Soriano, who opened the season as the closer, has been out since April 9 with a sore elbow. He was to begin an injury rehab assignment at Double-A Mississippi on Wednesday and pitch again with the club Friday.
ESCOBAR OUT: Shortstop Yunel Escobar remained sore and was held out of the lineup a day after colliding with Ryan Church on the final play of Tuesday's game.
Escobar, turning a double play at second base to end the game, threw to first while trying to jump and avoid Church's late slide. Escobar's knee struck Church in the head. Cox said Escobar might miss only one game.
Omar Infante filled in as the starting shortstop and leadoff hitter.