And former CFL quarterback Danny McManus can still see the telltale signs of blurry-eyed fatigue that set in on rookies when Week 13 rolled around in Canada with five games still left to play.
For those wondering what the effects might be if the NFL expands from 16 to 18 regular-season games, take it from those who've been through it: It's a grind.
"From week to week, game plan to game plan, there's the physical part, but the mental part of the preparation is what wears a guy down," said Newton, a former star offensive lineman, who began his pro career in 1984 with the USFL Tampa Bay Bandits. "You're going to blow a fuse. It's just bound to happen."
Newton got a taste of playing an 18-game season before going on to become a six-time Pro Bowl selection with the Dallas Cowboys.
McManus, who played for Florida State, spent 17 seasons in the CFL where 18-game schedules have been the norm since 1986.
"You'd see it around Week 13 through Week 16, these guys are just dragging themselves into the locker room," said McManus, who retired in 2006. "There's no doubt it's a grind to go 18 weeks. And we used to do it going 18 weeks straight."
These are among the sobering messages from several ex-USFLers and CFLers -- rounded out by Hall of Famer Jim Kelly, who broke in with the USFL's Houston Gamblers in 1984 before starring for the Buffalo Bills -- with firsthand knowledge of playing 18-game seasons.
All agreed the expanded schedules required a big adjustment from players.
And Kelly even wondered whether the NFL is using the 18-game schedule as a ploy in labor talks, which are now on hold after breaking down two weeks ago.
Ploy or not, the NFL went into negotiations with a desire to expand its regular season for the first time since going from 14 to 16 games in 1978.
In going to 18 games, the NFL would eliminate two preseason games in exchange for adding two regular-season games with the prospect of generating more revenue.
NFL players have balked at the proposal.
They've complained that an expanded schedule would increase the risk of injuries and, as a result, have the potential of shortening careers, thus cutting into their money-earning potential and reducing their retirement benefits.
Players also fear how much two more games would cut into their offseasons, which are already filled with mandatory and voluntary minicamps and workout programs from March to June.
The NFL did back off on its proposal in its last offer before talks broke down. The NFL proposed keeping the 16 regular-season games and four preseason games for two years, with any switch to 18 games negotiable.
Injuries, fatigue and weather conditions -- imagine how many fans would show up to a Week 19 mean-nothing game in January in wintry Buffalo, Kelly wondered -- were among concerns expressed by the each of 18-game veterans.
For Newton, an 18-game NFL schedule would require the league to expand its rosters from 53 to at least 60 players. And teams would be keen in stocking their lineup with at least two capable running backs and two quarterbacks to guard against injuries.