Johncock, 26, has returned home to Port Lincoln to attend the funeral on Friday and is expected to rejoin his teammates on Monday.
"Our thoughts are with Graham and the rest of the Johncock family at this difficult time," Crows chief executive Steven Trigg said in a statement.
Just three matches shy of the 150-game milestone, Johncock has impressed the club with his dedication over the summer following his demotion to the SANFL last year for failing to meet the necessary standards of preparation.
His absence this week could leave the door open for several young players, including Andy Otten and debutants Jared Petrenko, Myke Cook and Patrick Dangerfield.
Crows veteran Michael Doughty said the players would rally around the popular defender.
“Losing someone in your family, for anybody, is a pretty tough time, so we’ll give Graham all the support and time that he needs.”
