IRVING, Texas -- Former NFL coach Buddy Ryan was diagnosed with cancer last week according to his son, Dallas Cowboys defensive coordinator Rob Ryan.

Rob Ryan said his father has cancer in his glands that has spread to his neck.

Buddy Ryan said he's scheduled to have surgery Sept. 16 in Lexington, Ky., a few days after watching the Cowboys open their season at the New York Jets on Sunday night.

It's an important game for the Ryan family because Rob will face his twin brother, Jets head coach Rex Ryan.

"I'm going to be at the game and see my grandkids and I planned on staying longer," said Buddy Ryan, who is scheduled to arrive in the New York area Friday. "But I got to take care of some things."

From Jets camp, Rex added: "It's going to be great having him here. I know this is huge for him. He's looked forward to it for a long time."

Ryan said he would have to focus on the game for the time he is on the field, just the same as anyone trying to do a job while dealing with an issue like this.

"That's what everyone deals with, their own issues and things," Rex said. "But my job is to coach football and that's what I'm gonna do."

This isn't Buddy Ryan's first time battling serious health problems. He's overcome melanoma, a dangerous type of skin cancer, two times as well as encephalitis, an acute inflammation of the brain.

Ryan was also diagnosed with an undisclosed type of cancer this spring and overcame that as well.

"He knows this is a big thing for him and a big thing for the Ryans," Rob Ryan said. "He's about the only guy who's beat cancer about every time. He's been through it about four or five times so I'm sure the prognosis is great for him because he always wins."

Buddy Ryan was defensive coordinator of two renowned Super Bowl champions, the Joe Namath-led Jets who pulled off the huge upset in 1969, and the 1985 Bears who ran his 46 defense to perfection. He is also known for throwing a punch at the offensive coordinator while he was running the Oilers' defense. Ryan also had entertaining stints as the head coach of the Eagles and the Cardinals.

Both sons were on their dad's staff with the Cardinals in 1994 and '95. They've since made a name for themselves, with Rex Ryan leading the Jets to the AFC Championship Game the last two years, and Rob Ryan winning two Super Bowls as an assistant coach for the Patriots' Bill Belichick. This is Rob's first season in Dallas after working as defensive coordinator of the Browns and Raiders the last four years.

The brothers have squared off before, and every time is special for the Ryan family, especially the patriarch.

"This game's important to him," Rob Ryan said. "He wants to see these two rams butt heads."

Calvin Watkins covers the Cowboys for ESPNDallas.com. Information from ESPNNewYork.com's Jane McManus and The Associated Press was used in this report.