Publicly both the NFL and NFLPA have done as much as they can to present a unified front and to avoid a situation where they'll break down internally exposing a weakness for the other to attack.
It's possible that that weakness has already hit the players.
According to Daniel Kaplan of SBJ, there is a group of "as many as 70 players" who are close to signing with a law firm to intervene in the Brady v. NFL case. They're not looking to contest the case but they want a seat at the table. Kaplan reports that this group of players is said to be unhappy that mediation talks broke off last month in Washington D.C. The players decertified then and the owners locked them out shortly thereafter.
Kaplan reports this would be the first "evidence of [a] rift among the players." The NFL has 32 (wealthy) owners while the NFLPA has nearly 2,000 (not as wealthy) players so internal conflicts are much more likely with the players. I think that's something everyone knew heading into the lockout.
Last month NFL Commissioner Roger Goodell sent a letter to all NFL players describing the last deal the league had offered the union. It appeared Goodell was attempting to persuade the players their leadership turned away from a good deal and it also appeared the purpose of that letter was to fracture the players' unity getting them to question their own leadership.
Kaplan notes in his report that this is a group of "mid-tier" players hoping to file this motion with Judge Susan Nelson, perhaps as soon as this week.