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.