David Ortiz may not be the only Red Sox regular to start the season on the disabled list. Eleven days have passed since Stephen Drew was concussed by a pitch that struck him on the “B” of his batting helmet, and manager John Farrell said “the window has started to narrow” for the veteran shortstop to be ready for Opening Day. Drew has been cleared only to play catch, not to take batting practice or significantly increase his physical activity. Although he hasn’t experienced an increase in symptoms while riding a stationary bike, his vision is still impaired by what he describes as a “wavy” sensation. Because some symptoms have lingered longer than expected, Drew has been in daily contact with Dr. Michael Collins, director of the Sports Concussion Program at the University of Pittsburgh Medical Center. And before he returns to the field, Drew still must pass a series of concussion tests mandated by Major League Baseball. “When those symptoms are fully subsided is when he starts to ramp things up more intently, and we’re not there yet,” Farrell said before the annual St. Patrick’s Day matinee at JetBlue Park. “At some point you start to look. We’re getting into this last stage of camp. You’ve got to think about all the options.”