Preseason NFL football is about two things. First, a coaching staff wants to find the best players and fit them onto a 53-man roster. Second, everyone keeps their fingers crossed against injuries.In Thursday night's exhibition opener for the 49ers, a 24-21 win over the Dallas Cowboys at Levi's Stadium, the Niners suffered several injuries to key players – and some may keep those players off the field for a while.In just the first half, six players – including four starters and two important reserves – had to leave the game, according to Eric Branch of the San Francisco Chronicle: tight end George Kittle (shoulder), inside linebacker Malcolm Smith (hamsgtring), defensive tackle Solomon Thomas (concussion), running back Matt Breida (shoulder), outside linebacker Eli Harold (knee) and offensive tackle Garry Gilliam (concussion).Harold returned later, so he should be OK. But head coach Kyle Shanahan after the game told reporters he doesn't expect Kittle or Breida to practice or play this week.Said Shanahan of the injuries Thursday night: "It's what scares you about training camp. It's what scares you about the preseason. You kind of just want the game to end when...