Felix Doubront doesn’t want to be a one-year wonder. Last year, in his first full major league season, Doubront was the Red Sox’ best starter before the All-Star break. And although he tired during the second half, the 24-year-old lefty still finished with 11 wins and a 4.86 ERA. “I want to start out how I finished last year,” Doubront said after a voluntary workout here yesterday with his fellow pitchers. “Mentally and physically, I’ve said to myself I can do more than last year.” But manager John Farrell raised a caution flag when he revealed that Doubront and lefty reliever Craig Breslow will be “held back” during the first few weeks of spring training because of slight weakness in their throwing shoulders. Farrell stopped short of classifying Doubront and Breslow as “injured,” stressing that the Red Sox are trying to take precautions to avoid more serious problems. Last year, they took a similar approach with lefty Franklin Morales, who was healthy enough to be on the Opening Day roster. Doubront logged 161 innings last season, far surpassing his previous career high of 1291⁄3 innings in 2008 in the minors. But despite being shut down for two weeks in August because of some shoulder fatigue, he finished the season strong, posting a 3.08 ERA in his last four starts. And with pitchers and catchers set for their first mandatory workout today, Doubront seemed unconcerned about his health. “The goal for every year for every pitcher is the innings: more than 200 innings or close to 200 innings. That’s one of my goals,” Doubront said. “The first goal is to stay healthy and the second is probably the innings. If you do that, the rest comes — ERA, wins, losses.”