Nolasco, the Marlins Opening Day starter, is now 2-5 with a 9.07 ERA in nine starts.
"What I'm seeing is it looks like he's lost a little bit of belief in himself," Marlins catcher John Baker said. "It looks like he's pitching away from contact."
In a breakout 2008 season, Nolasco went 15-8 with a 3.52 ERA, racking up 212 1/3 innings. Aggressively, he attacked hitters, striking out 186 and walking only 42.
"We've got to get his confidence back," manager Fredi Gonzalez said.
The Marlins are in a deep slide since opening the season at 11-1.
With Friday's loss, they've lost three straight. Since that hot start, they are 8-23.
Along with optioning Nolasco, the Marlins made a series of moves Friday night.
Sean West will have his contract picked up from Double-A Jacksonville. The left-hander, who was a first-round pick in 2005, will make his Major League debut on Saturday night, getting the start against Tampa Bay.
Also, right-hander Chris Leroux was recalled from Double-A Jacksonville to provide depth to the bullpen.
Lefty reliever Dave Davidson was designated for assignment. Davidson pitched one inning on Friday, giving up five runs while throwing 52 pitches against the Rays.
Entering the season, the Marlins were optimistic because of their starting rotation. However, the starting pitching has labored thus far outside of standouts Josh Johnson and Chris Volstad.
Nolasco's two innings on Friday marked his shortest start since throwing two innings against the Brewers on Aug. 25, 2006, his rookie season.
The rotation also took a blow when right-hander Anibal Sanchez went on the disabled list on May 8 with a right shoulder sprain. Lefty Andrew Miller also spent time on the disabled list with a right oblique strain.
Miller is back now in the rotation.
Marlins first baseman Jorge Cantu can relate to what Nolasco is going through. In 2007, Cantu experienced a demotion to the Minor Leagues, and since then he's worked his way back.
"My best advice to him is to keep his head up and to battle through this," Cantu said. "I know what Ricky is capable of doing. I hope he can get through this, come back and be the Ricky of last year."