Mitchell has hamstring injury

49ers RB Elijah Mitchell has a hamstring injury that is expected to keep him out of the entire preseason, ESPN's Adam Schefter reports. "Mitchell is expected to be ready for the start of the regular season," Schefter adds. It's still disconcerting news, though, on a player that dealt with a bunch of different injuries as a rookie last year (although he had no hamstring trouble). We'll see when Mitchell is able to get back on the field. RB Trey Sermon drew the start in Friday night's preseason opener.