49ers Open Practice Window for WR Christian Kirk

• The 49ers announced the opening of Christian Kirk's 21-day practice window.
• Kirk has been sidelined since suffering a calf injury during training camp.
• Last season, Kirk caught 28 passes for 239 yards with a touchdown in 13 games for the Texans.
• Kirk's return could provide a boost to the 49ers' receiving corps.
• The practice window allows Kirk to gradually return to full football activities.