The news was earlier reported by FoxSports.com.
Keller tore his ACL, MCL and PCL and also dislocated his knee, a source familiar with the injury told ESPN NFL Insider Adam Schefter.
"I want everyone to know that as disappointing as this is I don't want anybody feeling sorry for me," Keller said in an email to NFL.com. "I promise I'm going to come back stronger, faster and be a better player than before. I'd like to thank all my family, friends and teammates for their prayers and support."
The Dolphins haven't provided any official word on Keller's injury.
Keller's leg bent unnaturally when he was tackled on the right knee by D.J. Swearinger on an incomplete pass Saturday night. He immediately grabbed his right knee and was soon carted off the field.
"With the rules in this era you've got to hit low," Swearinger told ESPN.com's Tania Ganguli after Saturday night's game against the Dolphins. "If I would have hit him high, I would have gotten a fine. So I think I made the smartest play. I'm sorry it happened and I pray he has a speedy recovery. ... Right now it's just instinct. You see somebody come across the middle, you gotta go low. You're going to cost your team 15 yards. You've got to play within the rules."
The rookie safety said he knew he had to change his playing style after being penalized for high hits in college.
"My senior year I had like three helmet-to-helmet [penalties]," Swearinger told ESPN.com. "I knew I had to change my style of play and start targeting low."
Swearinger also tweeted get-well wishes to Keller, although he identified him incorrectly as "Justin."
Keller spent his first five seasons with the New York Jets before signing a $4.25 million, one-year contract with the Dolphins in the offseason in hopes of proving that he's deserving of a long-term extension. He has 17 career touchdown receptions, but he played in only eight games in 2012 because of hamstring and ankle injuries.
He had one reception for 14 yards on Saturday.
His injury represents a significant setback for the Dolphins, who signed Keller to replace tight end Anthony Fasano and help second-year quarterback Ryan Tannehill. Keller and Tannehill had clicked in training camp and connected on a 22-yard touchdown pass in the second exhibition game.
Clay took to Twitter to wish Keller a quick recovery.
Praying my man @DUSTINKELLER81 has a speedy recovery....great ball player but even better person
— Charles Clay (@C42Clay) August 18, 2013
ESPN NFL Insider Adam Schefter, ESPN.com's Tania Ganguli and The Associated Press contributed to this report.