Washington was handed the hefty ban for yet another violation of the league's substance-abuse policy, having also been suspended for four matches of last season for similar reasons.
Keim described Washington's behaviour as "completely unacceptable" but insists that his team will cope with the 27-year-old's absence.
"It's completely unacceptable that Daryl has once again put us in this position. We all know what the consequences are and will deal with them," Keim said in a statement.
"From a personal standpoint, our hope is that this suspension will give Daryl the opportunity to accept the necessary help and guidance to get his life back on track and we will certainly support him however we can. As it pertains to our team, our approach is the same as it's always been - next man up.
"We talk a lot about how critical depth is to a team because situations always arise where you lose players, whether by injury or other circumstances such as this one. One player's absence is another's opportunity. That approach has served us well in the past and we will rely on it now."
Washington was elected to the Pro Bowl in 2012 having led the Cardinals in tackles for a second consecutive season that year.