Nava has struggled this season, posting a .130/.221/.234 slash line in 77 at-bats. He was optioned April 23 and made some adjustments to his stance, but has gone 0-for-10 in five games since returning last week.
"You go with who you feel is putting up your best at-bats a time," Farrell said when asked whether he would have liked to have gotten Nava more at-bats in his most recent recall. "The opportunities didn't present themselves as much for Daniel."
The 31-year-old had a .303/.385/.445 slash line in 134 games last season.
"When Daniel's right, it's one of the purest left-handed swings we have," Farrell said. "He's still working back to gain that consistency."
Farrell said he wanted to keep Alex Hassan's right-handed bat on the 25-man roster to balance the lineup, given how many lefties his team already has. Hassan was called up for the first time Friday when Ryan Lavarnway went on the 15-day disabled list with a left hamate (wrist) fracture that will require surgery.
Steven Petrella is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.