The breakthrough season the Cubs hoped to see from Jake Arrieta is already off to a slow start. During Thursday’s welcome-to-camp news conference, general manager Jed Hoyer revealed Arrieta felt right shoulder tightness when he started throwing this winter, a setback that makes him doubtful for the Opening Day rotation. “We’re going to be cautious with him,” new manager Rick Renteria said. “We wouldn’t expect that he would start the season with us.” As pitchers and catchers reported to the new Arizona complex, the Cubs had already taken out insurance policies, announcing one-year deals for Jason Hammel ($6 million) and James McDonald ($1 million, plus incentives, on a standard non-guaranteed contract for an arbitration-eligible player). Hammel, 31, has underwhelming career numbers (49-59, 4.80 ERA), but the Cubs liked how he battled in the American League East with the Baltimore Orioles and Tampa Bay Rays. He also competed at Coors Field, notching 10 wins and making 30 starts for the Colorado Rockies in 2009 and 2010. Right shoulder issues sidelined McDonald, 29, for most of last season. He went 12-8 with a 4.21 ERA for the Pittsburgh Pirates in 2012. The Los Angeles Dodgers named him their minor league pitcher of the year in 2007 and 2008.