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The angry bagel guy is now facing a big lawsuit after bailing on his "celebrity" boxing match with Dustin Diamond at the last minute.

According to new legal docs obtained by TMZ ... Chris Morgan is being sued by fight promoter Damon Feldman for $10,000. Damon claims Chris' change of heart cost him thousands of dollars in losses.

In the civil suit, the fight promoter claims Morgan signed a contract for a celebrity boxing match and pocketed appearance fees before pulling out of the fight.

You'll recall ... Chris surprised everyone hours before his Sept. 28 tangle with Screech, when he went on social media and said, "I fooled you all! I ain't coming to the fight."

Morgan left the promoter scrambling for a replacement, and filmmaker Matt Wolf ended up fighting Screech ... suffering a one-punch knockout at the hands of the "Saved By the Bell" star.