Trent Williams holding out of 49ers training camp for contract reasons

49ers left tackle Trent Williams is holding out of training camp.Head coach Kyle Shanahan said today that Williams is not present at the start of camp and that it's a contract issue."It was something I knew could be a possibility," Shanahan said. "I was hoping he would be here, but I knew it could be a possibility. I feel pretty confident it will all work out in the long run and he'll be here and we'll get on the same page with everything, but it's just one day of practice and I think Trent will be alright missing a few practices."Shanahan declined to go into any details about what Williams' issues are with his contract."A lot of things play into it but I'm not going to get into the personal parts of the contract," Shanahan said.The 36-year-old Williams has been a first-team All-Pro for three consecutive seasons, and the 49ers' offense would miss him if he held out for long. Williams is due a $20.05 million base salary this season and another $750,000 in per-game roster bonuses, but he has no guarantees left on his contract.