Manchester United central defender Ferdinand was last month charged by the FA over his "failure or refusal" to take a drugs test in September.
"It's crazy that Rio Ferdinand, after eight weeks, does not yet know if he's guilty or not guilty, or if he's going to be fined or suspended for one month or whatever," Eriksson told British newspapers on Tuesday.
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"I also don't understand, or agree with, the system for selecting players in those circumstances," added the England coach.
Eriksson was unable to play Ferdinand in England's final Euro 2004 qualifying game against Turkey in October.
He also had to discard Alan Smith from his squad for the 3-2 friendly defeat by Denmark on Sunday after the Leeds United striker was arrested over an alleged bottle-throwing incident in a League Cup match against Manchester United last month.