SARATOGA SPRINGS, N.Y. - For the second time in nine days, trainer Todd Pletcher had to cancel a scheduled workout for his top 2-year-old Overdriven, casting doubt over the colt’s ability to be ready for the Grade 1 Hopeful here on Sept. 5. Overdriven was scheduled to work four furlongs over Saratoga’s main track Thursday morning in company with Restitution. Pletcher didn’t like the way Overdriven was moving on the track and decided to have exercise rider Patti Krotenko gallop him about 1 1/2 miles. “He just doesn’t look quite right to me,” Pletcher said. “He seems fine but once you put a rider on his back he changes a little bit.”  On Aug. 9, Pletcher had planned to work Overdriven over the training track, but aborted that work when he didn’t like the way Overdriven warmed up. The colt was later diagnosed with a gluteal muscle pull that was internally blistered. The horse was back in training by the weekend. “We thought we saw some improvement,” Pletcher said. “It’s one of those things if you make a mistake it might be something you can’t undo.”  Pletcher was making arrangements late Thursday morning to ship Overdriven somewhere to undergo a nuclear scintigraphy to see if that reveals a problem.  Pletcher didn’t totally rule out Overdriven making the Hopeful but, said “we would obviously need everything to go just right at this point.”  Overdriven established himself as the leading 2-year-old on the East Coast with a 3 1/2-length maiden win at Belmont on July 1 and a four-length victory in the Grade 2 Sanford Stakes at Saratoga on July 24.