Blazers Gross has back ailmentPORTLAND, Ore fAPi - Portland Trail Blazers forward Bob Gross spent 10 days in traction in a hospital in early June with an undetermined disc problem in his back, Blazers trainer Ron CuId saidTuesday,Blazer officialshospitalizationCulp said the National Basketball Association team would conductmore tests on the five-year veteran's back to determine what is causing him painIf surgery proves necessary. Culp said Gross could be sidelined for as along as six months ■' 7^Gross was in Portland's Meridian Park Hospital resting in traction from late May to early June. Culp said.The Blazers are holding a rookie camp this week If Gross is sidelined, a berth could open at small forward where Coach Jack Ramsay said 6 10 David Lawrence from McNeese State. 6-9 Gig Sims from UCLA yr 6-10 Mike Harper from North Park College are the prime contenders C ' \ ^The Blazirs also released 6-6 Dave Kufeld from Yeshiva College on Tuesday Kufeld was their 10th round draft choice.