Seattle Seahawks cornerback Richard Sherman has claimed that he was racially abused by people on Twitter in the wake of his controversial comments about San Francisco 49ers receiver Michael Crabtree.

Sherman called Crabtree a "mediocre" player moments after making a crucial intervention to deny the wide receiver what would have been a match-winning touchdown in the closing stages of Sunday's NFC championship game.

The 25-year-old garnered widespread criticism for his post-match antics, some of which he says were of a racist nature.

"To those who would call me a thug or worse because I show passion on a football field - don't judge a person's character by what they do between the lines," Sherman wrote in a column posted on mmqb.com.

"Judge a man by what he does off the field, what he does for his community, what he does for his family. But people find it easy to take shots on Twitter, and to use racial slurs and bullying language far worse than what you'll see from me.

"It's sad and somewhat unbelievable to me that the world is still this way, but it is. I can handle it."

Sherman took to Twitter himself later, expressing his disappointment at the nature of the abuse he had received.

"Last night shows that racism is still alive and well... And that's so sad.... At Least some people respect MLKs dream," wrote the Pro Bowler.

Sherman has since apologised for his comments, saying that he should not have taken the focus off his side's achievement of reaching the Super Bowl.