Phillips, a sixth-round pick who contributed as a rookie last season, is out for the season.
Phillips' agent Jon Perzley said Phillips, who underwent the MRI test Monday morning, injured the knee Sunday night when he landed after catching a back-shoulder throw from Jon Kitna. It was the second of four receptions for Phillips, who left the game after he collapsed while battling with Cincinnati Bengals defensive end Frostee Rucker as he tried to release into a pass route.
"It's disappointing because he was having such a great camp and such a great game," tight ends coach John Garrett said after Sunday night's preseason win. "But I know one thing: He's got great resolve. He's got great perseverance. If there's anybody going to come back even stronger than he was before, it'll be John Phillips."
The Cowboys suddenly have no healthy tight ends behind perennial Pro Bowler Jason Witten. No. 2 tight end Martellus Bennett didn't play in the preseason opener to rest an ankle injury that sidelined him for the first week of training camp. Kevin Brock, who left Fawcett Stadium with a walking boot and crutches, suffered a left high ankle sprain after replacing Phillips. Undrafted rookie Scott Sicko suffered a concussion Sunday night.
Coach Wade Phillips said Monday afternoon that he had not seen the results of John Phillips' MRI, but the coach acknowledged that the Cowboys' personnel department is searching for tight ends to sign. The Cowboys hope Bennett will play in Thursday night's preseason game against the Oakland Raiders.
The Cowboys announced the results of the MRI soon after Wade Phillips' news conference. John Phillips will undergo surgery after the Cowboys return from training camp in Oxnard, Calif.
Phillips blocked well as the Cowboys' third tight end during his rookie season, when he caught seven passes for 62 yards. His progress as a receiver and ability to be a lead blocker out of the backfield made it a strong possibility that he'd have an increased role in the offense this season.
Phillips tore the ACL in his left knee at Bath County High School in Hot Springs, Va. He had a feeling Sunday night that he did the same thing against the Bengals.
"He understands the business and what's it about," Perzley said. "The kid told me it took him four months to recover [from the the high school injury]. He's a man of steel. Everybody is in shock around here."
The Cowboys are also thin at cornerback due to a couple of injuries Sunday night. Cletis Gordon, the front-runner in the competition to be the Cowboys' fourth cornerback, strained his neck on a punt return during the second half and will be further evaluated. Undrafted rookie cornerback Bryan McCann suffered a chest contusion on another punt return. Wade Phillips said the Cowboys are also considering signing a cornerback or two.
Alex Barron, the backup at both offensive tackle spots, also left the game after spraining his left ankle. Wade Phillips said he didn't think the injury was serious, adding that Barron might be able to play Thursday.
Calvin Watkins of ESPNDallas.com contributed to this report. Tim MacMahon covers the Cowboys for ESPNDallas.com. You can follow him on Twitter.