Jorge Mateo, one of the A’s most promising prospects, will not get as many at-bats early in the spring as the team had hoped because of a lingering knee problem. Mateo sprained the ligament in his left knee during winter ball and is still having some minor issues, particularly when it comes to decelerating. The shortstop is considered the fastest player in Oakland’s system, so running is a crucial part of his game; he’ll be held out of Cactus League action at least initially but he is participating in most of the team’s on-field work, including hitting. “The issue he has is slowing down - and he gets going pretty fast,” A’s manager Bob Melvin said Tuesday morning at Fitch Park. “This time of spring, we’re going to be conservative, especially with a guy like him.”