Walker reported to the team's Alameda facilities Tuesday complaining of pain in his abdomen. Team trainers initially believed Walker was suffering from an appendicitis attack until further tests revealed the fourth-year pro was bleeding internally.
Walker was then taken to a nearby hospital where he underwent surgery Tuesday afternoon. He is expected to remain hospitalized 4-5 days, according to Turner.
''It's a serious deal,'' Turner said. ''He is OK. That was the number one concern. It's unfortunate for our football team but he's fortunate he's all right.''
Walker started all six games for the Raiders this season but came out for a few plays of last Sunday's 38-17 win over Buffalo. Oakland's players came in for meetings on Monday and Walker gave no indication that he was hurt, other than to complain about irritation in his abdomen.
A day later, however, Walker's situation turned serious and he was quickly taken in for surgery before it could turn life-threatening.
''It was fortunate they got to it before that point,'' Turner said. ''My understanding is that it could get to that point very quickly.''
With Walker out, the Raiders had to do some scrambling with their offensive line. Brad Badger, who would seem to be the logical replacement for Walker, was limited in practice due to a knee injury that has him listed as probable on the team's injury report.
Jake Grove, the team's starting center who has been out since Oct. 2 due to a right knee injury, took most of the reps at left guard Wednesday. Grove started eight games at right guard as a rookie before moving back to center this season.
With Grove working at guard, veteran Adam Treu continued to handle the reps at center.
* Wide receiver Randy Moss practiced and seems to be making progress after suffering a triad of injuries in the loss to San Diego Oct. 16. ''He's probably about where he was on game day,'' Turner said. ''He took his normal share of reps but I don't think he was able to cut it loose.''
* Ronaldo Hill and Jarrod Cooper split time working at strong safety, the spot left vacant due to injuries to Charles Woodson and Derrick Gibson. Hill is likely to start while Cooper provides Oakland the physical match-up that Woodson and Gibson did.
* Calvin Branch, signed last week, is likely to be activated against Tennessee and will play on special teams. Turner said Branch might also get some playing time at safety, given Oakland's injury-riddled secondary.