The little, nagging injuries are starting to pile up on the Mets this spring, and now they are looking at one that could affect the start of the regular season. With Jacob deGrom suffering lower back stiffness and having his throwing program slowed down, Mickey Callaway admitted they do not know if they will have time to stretch him out enough for the start of the season. “We are probably not totally clear on that yet,” the first-year Mets manager said. “We’ll have to see how his throwing progression goes and kind of go from there.” DeGrom said he hopes to throw a modified bullpen session on Wednesday and then would need one more bullpen session before he would be ready to pitch in a spring training game. Callaway said that five spring starts would probably be the minimum for the starters to be ready. DeGrom would need to be in a game by Sunday to get five spring training starts before Opening Day. After spending all winter talking about the health of their pitching staff, you would think the Mets would err on the side of caution with their best pitcher over the past three years. “I think that five is the minimum number if you had to put a number on it,” Callaway said. “Everybody is different. When you are making out a spring schedule for a pitcher, the goal is to just make sure it’s a progression. Another goal is to worry about how many pitches you want him up to. Some people start the season having been stretched out to 75 pitches. So maybe five outings OK. Others want to get that sixth outing to get to 100. It’s really based on the guy and who he is.” DeGrom is the first of the injuries that the Mets have to worry could possibly affect the season. They added Yoenis Cespedes to the list Tuesday with a sore right shoulder, but the Mets slugger downplayed it as an annual issue as he begins to throw hard. Cespedes, who hit a three-run homer on Sunday as a DH, said he expects to be back in the lineup on Friday. “It’s something that I am not worried about,” the slugger said. “Every time, every season, it gets like this. I spend the whole offseason without throwing the ball. It’s not something I should be concerned or worried about.” Right-handed reliever Anthony Swarzak is headed to the MRI tube after he felt his left calf “grab,” as he pushed off to run over to first. The Mets reliever, however, was not very concerned about it being a long-term issue.