While John Farrell has only given official word now, this should come as no surprise to either man. The manager had already revealed a while back that he foresaw using Daniel Nava in the lineup against some right-handed pitchers, forming something of a pseudo-platoon with Jonny Gomes once David Ortiz' health problems sort themselves out. And while Jackie Bradley Jr. may have taken away his starting job in left field for the immediate future, Nava is certainly valuable as a back-up given his abilities from the left side of the plate.
Mortensen's spot in the bullpen was almost guaranteed when Daniel Bard was optioned to Portland. He will likely function as the mop-up man in games that get out of hand one way or another.
Meanwhile, the hold-up on Jackie Bradley Jr. seems to be that the young outfielder lacks a spot on the 40-man roster. There are enough fringe names on that list that the Sox shouldn't have much problem finding a place for him, however. They'll take as much time as possible to make up their minds, but however much John Farrell hedges his bets it seems certain he will have a spot by Monday.