In "League of Denial: The NFL, Concussions and the Battle for Truth," written by investigative reporters Mark Fainaru-Wada and Steve Fainaru, the NFL is portrayed as an organisation that exerted its influence in an attempt to sweep aside independent research and fund studies of its own on the cumulative impact of hits on the football field.
The authors write that the denials started in 1994 with then-commissioner Paul Tagliabue and continue today with present commissioner Roger Goodell.
New England Patriots tight end Rob Gronkowski has yet to play this season and still isn't sure when he'll be on the field, but he emphasised there's no pressure from the team to hurry back.
Gronkowski has been practicing on a limited basis as he recovers from forearm and back injuries.
"It's going good," Gronkowski said. "I'm progressing every week, feeling better every week, getting stronger every week, getting in better condition every week. So I'm still sticking to the motto day by day."
Offensive tackle Levi Brown will be traded from the Arizona Cardinals to the Pittsburgh Steelers pending a physical.
Brown, owed more than $3.6 million, is signed through 2014.
His salary next season is $6 million.
Wide receiver Tiquan Underwood has signed with the Tampa Bay Buccaneers after the release of Kevin Ogletree.
Underwood played at Rutgers under coach Greg Schiano, now at Tampa Bay's helm. He was drafted by the Jacksonville Jaguars in 2009 and spent time with the New England Patriots and Buccaneers.
San Francisco 49ers running back LaMichael James has used Twitter this week to vent his frustration over playing time this season.
With Frank Gore entrenched as the starter and Kendall Hunter as his back-up, James was inactive for the 49ers' first three games. He had three carries for zero yards against the St. Louis Rams in Week 4.
"Some things I just don't understand at all I don't work at State Farm I'm not trying to be insurance," James tweeted.
He later deleted the tweet but added, "I don't tweet bout football on anything to my team so don't need ur input."
The San Francisco 49ers announced they have signed former Arizona quarterback John Skelton to a one-year contract.
Skelton, 25, spent three seasons with the Cardinals and started 17 games, posting an 8-9 record. He was waived by the Cardinals on April 1 and picked up by the Cincinnati Bengals.
But he failed to survive the final round of cuts in training camp with the Bengals.
Skelton is expected to compete with Colt McCoy for the backup quarterback job behind starter Colin Kaepernick.