The Red Sox are allowed to fill that roster spot, and manager John Farrell said the team will likely use it for a pitcher.
This could allow right-hander Brandon Workman, who is transitioning to the bullpen and ranked the club's No. 11 prospect, to be called back up.
Workman, who was solid in his first three Major League starts for the Red Sox, was optioned to Triple-A Pawtucket on Thursday, mainly because Boston's bullpen was spent from a 15-inning game the night before.
Under normal circumstances, Workman would have to stay in the Minors for 10 days. However, he is eligible to replace a player who is placed on the disabled list, or, as in Nava's case, the paternity leave list.
Workman was scheduled to make his first relief appearance for Pawtucket on Sunday.
"It's not a scripted outing of, 'OK, it's two innings today.' We're going to kind of let this now work out of the bullpen with what the game might dictate," said manager John Farrell. "Hopefully it's a clean inning he comes in to start with. If not, we're not going to hold him to that, or hold the staff to that."
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. Michael Periatt is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.