TAMPA, Fla.—Mark Teixeira returned to Yankee camp Sunday for the first time since injuring his wrist in the World Baseball Classic—and immediately disclosed that his injury is not quite what the Yankees had announced, stoking fears that he could be out far longer than the initial eight-to-10-week prognosis or hindered all year if he does return on time.

Mark Teixeira has a partially torn tendon sheath, not a strained tendon in his wrist. Associated Press

The team had initially announced that Teixeira had a strained wrist tendon, an injury that should heal with rest. But Teixeira, on his return to the Yankee complex, said that he actually has a partially torn tendon sheath, a more ominous injury that has felled several stars in the past few years.

"It's the tendon sheath that holds the tendon over," Teixeira said. "It's just the little covering that holds the tendon in place —the tendon will snap in and out if the sheath is gone. If that doesn't heal, then the tendon has a chance to get damaged, and you don't want that."

That's exactly what happened to Toronto star Jose Bautista last season. He injured the tendon sheath, tried to come back too early, and was shut down for the season with an unstable tendon. Teixeira is very aware of that danger.

His timetable for return has generally been pegged at early May, but if it turns out to be early June, Teixeira said, so be it. Teixeira wants to ensure enough time has passed that he doesn't have lingering problems.

"If I try to play too early from this, we could miss the whole season, and we don't want that," Teixeira said. "I don't know if it's the beginning of May, the end of May, the beginning of June. I don't know when it is, but we've got a whole bunch of season left, and the time that really matters is the playoffs."

Even the cautious approach won't knock out the problem completely, however—Red Sox slugger David Ortiz suffered the same injury in May 2008 and returned without surgery, but was still complaining of discomfort that winter.

The two-month timetable probably won't be enough time to heal fully, said Dr. Michael Hausman, an orthopedic surgeon and chief of the hand and elbow service at the Icahn School of Medicine at Mount Sinai Medical Center in New York. The first baseman could return to action, but still feel the effects of the injury for much of the season.

"I think a total recovery, until you've plateaued and you're as good as you're going to be, that's more than a two- or three-month process. But I would think that he would be able to play, and play effectively, after about 10 weeks or so."

Teixeira's admission Sunday caused some confusion in the Yankee front office. After Teixeira disclosed that the problem was with the tendon sheath, Yankee general manager Brian Cashman called team doctor Christopher Ahmad to sort out the conflicting reports—and Ahmad confirmed that the sheath was in fact the issue.

The good news is that the underlying tendon is stable, Cashman said. When Bautista reached the point where both the tendon sheath was torn and the tendon was unstable, surgery became a necessity.

As Teixeira's tendon is unaffected, Cashman said that this new diagnosis doesn't change the timetable for recovery—it's still eight to 10 weeks.

But if the injury doesn't heal in that period, Teixeira could be a candidate for season-ending surgery; Cashman said there's a 25% to 30% likelihood that's the case.

The stable tendon offers a good chance that time and rest will be enough to fix the problem, Hausman said.

"If it's a partial tear where there's not enough structural damage where the tendon is actually popping out of its groove, then you're really just dealing with the issue of pain control… and allowing it to heal enough that it's not weakened and at risk for future rupture," Hausman said.

Write to Daniel Barbarisi at Daniel.Barbarisi@wsj.com