MILWAUKEE -- Last year, the Brewers gathered for Spring Training with some certainty at one infield corner and some questions about the other. That apparently will be the case again in 2007, only the roles are reversed.

Coming off a solid rookie season, first baseman Prince Fielder will be back for his sophomore season looking to build on a 28-homer, 81-RBI effort. But across the diamond at third base, the Brewers remain in limbo with third baseman Corey Koskie, who did not play after last July 5 because of post-concussion syndrome. His uncertain status for 2007 has the team "concerned, but not alarmed," according to the club's top medical official, and ultimately unsure who will man the hot corner on Opening Day.

"He is progressing in a positive direction, but no baseball activities yet," said assistant general manager Gord Ash, who got an update on Koskie from head athletic trainer Roger Caplinger on Tuesday. "The information we have is somewhat vague, and I don't know that we'll know anything more until we see him in person."

That means the Brewers will head to Maryvale Baseball Park with no definitive third baseman. According to Ash and general manager Doug Melvin, top prospect Ryan Braun is one option to replace Koskie, and the team also could look to veteran backups Craig Counsell or Tony Graffanino. No one on the free agent market has piqued the Brewers' interest.

"We're always keeping our eyes open, but there's no need to panic just yet," Ash said.

Koskie was acquired at a discount last January from the Blue Jays, who had a glut of corner infielders, and agreed to pay much of his salary in 2006 and 2007. He batted .261 with 12 home runs in his first 76 games but was injured on July 5, when he teamed with shortstop Bill Hall for one of the more jaw-dropping defensive efforts of the 2006 season. Koskie drifted into foul territory after a Felipe Lopez popup and attempted a sliding catch. Koskie adjusted mid-slide and actually gloved the ball, but as his body hit the ground the baseball popped straight up into the air, where Hall plucked it on the run.

Inning over. The Brewers later overcame a pair of extra-inning deficits and beat the Reds on a Rickie Weeks single in the bottom of the 13th inning, finishing a three-game sweep.

"It seemed like such a harmless play," Koskie said later.

It proved anything but harmless. Koskie later left that game with dizziness, and, still feeling nauseous and out of sorts after the All-Star break, he underwent a CAT scan and a battery of tests before the Brewers' second-half opener in Arizona. The team's athletic trainers first ordered some physical exertion, then tested Koskie in a series of mental exams. Koskie couldn't remember simple series of words and was placed on the disabled list.

Milwaukee Brewers • Catchers: Miller set to spell Estrada • Corner IF: Questions linger at third • Middle IF: Duo aims for solid year • Outfielders: Eyes on Jenkins, Hall • Starters: Rotation appears to be set • Bullpen: Cordero has solid support • DH/Bench: Veteran duo leads group

Doctors, including a specialist in Pittsburgh, diagnosed Koskie with post-concussion syndrome, a mysterious ailment that also struck Giants catcher Mike Matheny and Cardinals center fielder Jim Edmonds during the 2006 season. There is worry in San Francisco that Matheny's career, which began in Milwaukee, is over.

"The doctors told us right from the beginning that he would improve, it was just a matter of when," Ash said of Koskie just after the season. "The 'when' obviously took much longer than anybody had envisioned."

Koskie has been participating in Pilates and weight training, but continues to experience symptoms of post-concussion syndrome, Ash said. Koskie is signed through 2007 and the Brewers are on the hook for $2 million of his $5.85 million salary.

Asked late in the season for his take on Koskie's situation, manager Ned Yost said, "I just don't know. I don't think anybody knows.

"We just have to play it by ear and keep our fingers crossed, hope he comes into Spring Training ready to go," Yost said. "We're dealing with a lot of unknowns here. Who would think that he would miss the whole second half because of that? I never dreamed it. I thought he would miss a week or 10 days, but not the whole second half."

Repeated attempts to reach Koskie since the end of the season, including several calls within the last week, have been unsuccessful.

At first base, the Brewers are set with Fielder, who batted .271 in his rookie year and finished the season with 35 doubles, 28 homers, 81 RBIs and 82 runs scored, second in all categories to team MVP Hall. But after winning National League Rookie of the Month honors for April and carrying a .288 average into August, he tailed off. Fielder batted .230 over the final two months with eight homers.

Yost believes that Fielder's personal struggles had a lot to do with the Brewers' team-wide slump that followed Carlos Lee's trade to Texas on July 28.

"When you're a pretty talented offensive performer, you try to raise your game up to help out," Yost said during the season. "In essence, you start pressing a little bit to make things happen, and that's when you come out of your approach. [Fielder] started swinging at pitches he normally wouldn't swing at."

Brewers pitchers and catchers must report to Maryvale Baseball Park by Feb. 17. Position players report by Feb. 23.