Thomas, who has experienced back problems in the past, suffered the injury in Sunday's 27-17 loss to the New York Giants.
"This past game he felt a little numbness and tingling in his legs, so we sent him to a specialist," Reid said yesterday at a news conference at the NovaCare Complex.
Actually, the Eagles sent Thomas to two specialists. Both recommended that the 6-foot-7, 349-pounder have the procedure.
Thomas will be replaced by rookie Todd Herremans, a fourth-round Eagles draft choice out of Saginaw Valley State. The 6-6, 321-pound Herremans will be seeing his first NFL action after not being activated for the first 10 games. He did start three of the Eagles' four preseason games for Thomas, who was recovering from a blood clot in his leg.
"You never want anybody in front of you to go down, but when the opportunity comes, you make the best of it," Herremans said yesterday after practice. "Tra will get everything taken care of and have a great recovery, and he will come back and be a great player."
This has been a difficult season for Thomas, 31. He missed both minicamps in the off-season after being diagnosed with the blood clot.
Before this season, Thomas had missed just one game because of injury, against Miami in 2003 due to back spasms.
The Eagles' first-round draft choice in 1998, Thomas has started 118 of 119 regular-season games, including all 10 this season and 12 postseason contests. He had one of the most difficult jobs in football, blocking for the quarterback's blind side.
Thomas, who signed a six-year contract extension in 2003 that included a $6 million signing bonus, is signed for three more years. His base salary for this season, which included an already attained bonus, is $3 million. The base salaries increase to $3.65 million next season, $4.55 million in 2007, and $5.45 million in 2008. Approximately $1.6 million of the signing bonus is still on the Eagles' future salary caps.
Reid said the doctors indicated that the surgery should fix all of Thomas' back problems. But the coach added: "What I have learned here . . . is that you are never sure when you are dealing with backs. They feel pretty good about it and we will just have to see how the recovery process goes."
Reid did have one prediction. "He should be able to go for the minicamps," he said.
Thomas has been bothered by a back problem this season, but Reid said one couldn't tell by the way Thomas was playing.
"I think he was having a good year, so I didn't think it affected him too much other than when it was bothering him," Reid said. "It seems to take a week to get rid of it and then he was ready to go again."
The Eagles' offensive line has taken some major hits lately. Center Hank Fraley was lost for the season with a rotator-cuff injury after eight games. Guard Artis Hicks, who suffered a knee injury last week against the Giants, is listed as doubtful for tomorrow's game at Lincoln Financial Field against the Green Bay Packers.
Adrien Clarke, who played nearly three full quarters in place of Hicks on Sunday, appears ready to make his first career start.
"Right now if he had to play, he couldn't play," Reid said of Hicks.
The 6-5, 330-pound Clarke was a 2004 seventh-round pick from Ohio State who missed last season with a torn hamstring. He also played most of the second half in the Eagles' 37-31 win over Kansas City on Oct. 2 after Hicks was sidelined with an ankle injury.
"It helps that I got to play a lot last week and get warmed up," Clarke said. "It felt good to play and I'm trying to keep the ball rolling."
In other moves yesterday, the Eagles promoted guard Scott Young and quarterback Andy Hall from the practice squad. The moves continued a trend that has made the Eagles' offensive line one of the team's most inexperienced units.
The notable exceptions include right tackle Jon Runyan, who has started all 90 regular season games he has appeared in for the Eagles. Runyan is in his 10th NFL season and his sixth with the Birds.
Starting guard Shawn Andrews, who missed his rookie season with a fractured right fibula, is the next senior member with 10 career NFL starts.
"I feel like a grandfather out there," Andrews quipped.
Runyan put Thomas' loss in perspective.
"It [stinks]," he said. "It is something you have to deal with and all you can do is move on."
Contact staff writer Marc Narducci at 856-779-3225 or email@example.com.