Campbell received a concussion on the play, and has not practiced since. He will not play this Sunday when the Browns play Jacksonville.
Gay was not penalized for the hit.
"I thought he got hit in the face mask right from the beginning and then obviously you see the replay and it's really easy to see from all the angles except the one that the referee had -- he's standing behind," Browns offensive coordinator Norv Turner said.
"You'd just like someone to come in and help him make that call. The way it's being emphasized by the league, it should never be missed. And the ones that they've made mistakes on is where they've gone too far. So this one obviously they didn't go far enough."
The NFL said that Gay was fined for "unnecessarily delivered a forcible blow to his opponent head and neck area."
Gay's base salary is $1 million, or $58,823 per week. So he lost about one-fourth of his weekly pay -- before taxes.
In other fines around the league Friday:
• Chicago Bears guard Kyle Long and fullback Tony Fiammetta were each fined $7,875 for their involvement in a scuffle with St. Louis Rams players. The Rams' Chris Long wasn't fined for leaving the bench to break up the fight involving his brother.
ESPN.com Browns reporter Pat McManamon, Lions reporter Michael Rothstein and Texans reporter Tania Ganguli contributed to this report.