Bell is going through a rough spell, having saved three of six chances. Technically, he wasn't tagged with a blown save Wednesday night, but he was charged with the two runs the Giants scored in the ninth inning to set up extra innings.
Steve Cishek inherited Bell's runners, but minimized the damage, and the Marlins won, 3-2, in 10 innings.
Neither Bell nor Cishek were available for Thursday's series finale with the Giants.
Edward Mujica and Ryan Webb were the first options if there were a save opportunity. The Marlins are hoping to also rest Cishek on Friday, when the team is at San Diego.
"I wish I can stay away from Cishek for a couple of days," Guillen said. "We need him, but this guy's career is more important than winning another game."
The Marlins signed Bell to a three-year, $27 million deal last December. While with the Padres from 2009-11, Bell's 132 saves were the most in that span.
"I've told people, we are a better team with Bell closing," Guillen said. "There's no doubt. That's what we want. That's what I want. I never manage it for the fans. I never manage it for the owners. I manage it for the ballclub. Obviously, we need wins."
Physically, Guillen says Bell is fine. His velocity has been between 92 and 94 mph.
"I worry about location and I worry about strikes. Arm strength is fine," the manager said. "The ball is coming out of his hand pretty good.
"He's throwing the ball good, but he's not getting people out. It's not easy to have patience. It's not easy to lose games that way, but we are a way better ballclub with him as a closer."
Guillen understands people's impatience.
"It drives me crazy more than anybody else," he said. "I'm the one who put him there. I'm the one who takes him out. I'm the one who is taking the blame. All those people worry about it, relax. Chill."