Crowell said he made an "extremely poor decision" when he posted a drawing that graphically showed a hooded individual putting what looks like a machete into the throat of a police officer.
The Browns organization did not mince words in reaction to Crowell's post.
"We have spoken to Isaiah regarding his extremely disturbing and unacceptable social media decision. It was completely inappropriate and we have made him aware of our high level of disappointment," the team said in a written statement. "Isaiah has apologized but also knows that just an apology is insufficient and that he must take steps to make a positive difference after a very negative and impactful post."
"It was an extremely poor decision and I apologize for that mistake and for offending people," Crowell said in a statement released by the team. "My values and beliefs do not match that image."
The post went up after the police killings of Alton Sterling in Baton Rouge, Louisiana, and Philando Castile in Falcon Heights, Minnesota, and before the killing of five Dallas police officers Thursday night.
Stephen Loomis, president of the Cleveland Police Patrolmen's Association, also was critical of Crowell, telling TMZ Sports that the player's "store-bought apology" was inadequate.
Cleveland police chief Calvin Williams said that Crowell apologized to him in a call Tuesday, and that Crowell said he was caught up in the emotion of last week.
Crowell wrote that he was "outraged and upset" by the killing of Sterling and Castile, and "outraged and saddened" by the killing of the five Dallas police officers. He called last week "an emotional and difficult week," but said his post was wrong.
"We have to be better as a society," Crowell said. "It's not about color, it's about what's right and wrong. I was very wrong in posting that image. Every single life matters, every death as a result of violence should be treated with equal outrage and penalty."
Crowell removed the image shortly after posting it, but the image still was shared on social media.
NFL spokesman Brian McCarthy, when asked if the league had any response, said: "The image was inappropriate and insensitive. He realized this, took down the post and has since apologized."