Nationals manager Davey Johnson said before Friday's game that Suzuki is a No. 1 catcher and welcomed his veteran presence.
Suzuki, 28, was batting .218 with the Athletics this season and is owed more than $6 million for 2013.
The Nationals have been looking for catching help to complement Jesus Flores. Wilson Ramos has had two knee surgeries since first hurting his right knee on May 12. Ramos was acquired from the Twins in a June 2010 trade that sent Matt Capps to Minnesota.
Freitas might be a full year away, and has been playing for the Nationals' Class-A affiliate.