Every member of the Red Sox saw the play that injured Jacoby Ellsbury. But until they got to their clubhouse, they did not realize quite how serious and how alarming it really was. Player after player was made uncomfortable just at the sight of Rays shortstop Reid Brignac‘s knee driving into the back of Ellsbury’s shoulder as the Red Sox leadoff hitter — who was running on the full-count pitch, and thus in position to take out Brignac’s legs — slid hard into second base in a futile attempt to break up a double play.

Aside from diagnosing the obvious — a right shoulder injury — the Red Sox had no further word (at least officially) about the precise nature of the injury. But one player’s description of the word inside the Sox clubhouse was revealing.

“The only thing we’ve even heard is probably the same thing that everyone has been hearing, which is that it felt like something moved a little bit,” Kevin Youkilis relayed.

Obviously, movement inside of a shoulder is potentially very, very bad news for the Red Sox. One orthopedist, who had no direct knowledge of Ellsbury’s case, nonetheless saw the replay and heard Youkilis’ description and suggested it was difficult to consider the forecast for the runner-up in last year’s AL MVP balloting anything but severe.

Dr. Christopher Geary, the head of sports medicine at Tufts Medical School, said that the injury looked like “either a shoulder subluxation or a torn rotation cuff. I would think six to eight weeks best case.”

UPDATE: An industry source with knowledge of the situation confirmed Geary’s analysis, and said that Ellsbury likely had suffered a subluxation or dislocation of his shoulder.

That best-case scenario would involve a course of rest and rehab. It is worth noting that Derek Jeter suffered a similar injury on Opening Day in 2003, when Blue Jays catcher Ken Huckaby landed on his shoulder on a play at third base. Jeter rehabbed and was back in six weeks, and performed at an exceptional level (.324 average, .393 OBP, .844 OPS) in 119 games that year.

However, Geary also noted that sometimes rehab isn’t enough with shoulder injuries, and surgery becomes necessary. In such a scenario, he said, Ellsbury could be out for the year.

Until more specifics about Ellsbury’s injury become available, there remains a chance that his injury is less severe than it appeared. That, at least, is the hope of his teammates.

“You’re not going to get any better by losing him for a while,” said David Ortiz. “Hopefully things don’t go the way it looked like in the video.”

That said, every proclamation by a player that the Sox hoped for the best was tinged with another reality — namely, that there was an undeniable reality involving potential worst-case scenarios that would leave the Sox without one of their best players for weeks, months, perhaps even the year.

In that respect, it was difficult to avoid the echoes of the 2010 season, when Ellsbury collided with Adrian Beltre in the sixth game of the year and for all intents and purposes was lost for the rest of the year. This time, an injury incurred in the Sox’ seventh game may or may not prove as damaging, but for the Sox, until the precise diagnosis and prognosis are established, the team will have little choice but to hold its collective breath about an injury that has the potential to alter the course of the season.