Playing without Ramirez and outfielder Andre Ethier, still sore from fouling a ball of his right foot on Saturday night, the Dodgers lost to the Braves, 8-1, on Sunday afternoon.
While Mattingly didn't have Ramirez's MRI results after the game, it sounded like a roster move was coming on Monday.
"We can't continue to play short," the manager said. "You can't play the National League game like that. We can't continue to do this. If you can't play, for me, you have to be on the DL. We can't be trying to hang on and give a guy an extra three days. If you play short in this league, you're just giving games away. That's what we're trying to do. If you can't play, you just can't play."
Ramirez delivered a pinch-hit RBI single in the eighth inning of Saturday's 2-1 loss to the Braves, but was immediately removed for pinch-runner Clayton Kershaw.
"If you can't play full speed, it's tough, especially if he's playing short," Mattingly said of Ramirez. "He can hit, but he can't run."
Ramirez played in three rehab games, including one as the designated hitter, with Class A Rancho Cucamonga last weekend before he was activated. But by Thursday, his hamstring was again causing problems.
"I think the players really have to push themselves in the rehabs to the point where, can you go full speed or not?" Mattingly said. "I think you go the Minor Leagues and you don't play full speed and you think, 'Oh, I'm ready.' And then you get here and you try to go full speed. Not saying this is anybody's fault; it's just the reality of what's going on."
Kemp suffered a setback during a workout to test his strained right hamstring on Sunday morning.
Kemp, who had been rehabbing in Arizona at the Dodgers' Spring Training facility at Camelback Ranch-Glendale before Sunday, worked out on the field at Dodger Stadium under the watchful eyes of the team's medical staff. The All-Star stretched, ran sprints and did a variety of agility drills. But his hamstring bothered him and the Dodgers don't anticipate activating Kemp when he's eligible on Friday.
"We've hit a little bit of a snag, because he felt just a little something today still," Mattingly said. "He's still not there yet. We're not where we need to be with him. We do know that he's not 100 percent."