The other players the Sox have protected for the Rule 5 Draft are catcher Dan Butler, outfielder Alex Hassan, right-hander Alex Wilson, catcher Christian Vazquez and knuckleballer Steven Wright.
To make room for those players, Boston designated five players for assignment -- infielder Ivan De Jesus, third baseman Danny Valencia, and right-handed pitchers David Carpenter, Sandy Rosario and Zach Stewart.
Stewart was the prospect the Red Sox acquired for Kevin Youkilis back in June, but he struggled mightily in two Major League starts.
Webster, a sinkerballer, is someone Boston hopes can be a big part of the organization's future.
Last season, he went 6-9 with a 3.86 ERA and 129 strikeouts while walking 61 over 29 appearances.
Butler is known for his defense at a position the Red Sox can't afford to lose depth at within the organization. The same goes for Vazquez, who doesn't have the same experience as Butler, but is considered by some to be Boston's best defensive catcher in the Minors.
It was viewed as somewhat of a surprise that the Red Sox protected Hassan, a 20th-round pick out of Duke in the 2009 First-Year Player Draft, who had some health problems late in 2012. However, he is one of the most disciplined hitters in Boston's farm system. He had a .377 on-base percentage for Triple-A Pawtucket last season while drawing 55 walks.
Wilson's stock has risen since the Red Sox converted him to the bullpen. At Pawtucket in 2012, he produced 78 strikeouts in 72 2/3 innings while sitting in the mid 90s with his fastball. He could be an option in the Majors as a closer at some point.
Wright, 28, was acquired by the Red Sox from the Indians for Lars Anderson last July 31.
The Rule 5 Draft takes place on Dec. 6 in Nashville, Tenn. Before that, another key date on the offseason calendar awaits. By Nov. 30, the Red Sox must tender contracts to all of their unsigned players.
Here is a look at Boston's updated 40-man roster:
PITCHERS (23): Alfredo Aceves, Scott Atchison, Andrew Bailey, Daniel Bard, Pedro Beato, Craig Breslow, Drake Britton, Clay Buchholz, Chris Carpenter, Rubby De La Rosa, Felix Doubront, Rich Hill, John Lackey, Jon Lester, Mark Melancon, Andrew Miller, Franklin Morales, Clayton Mortensen, Stolmy Pimentel, Junichi Tazawa, Allen Webster, Alex Wilson, Steven Wright.
CATCHERS (5): Dan Butler, Ryan Lavarnway, David Ross, Jarrod Saltalamacchia, Christian Vazquez.
INFIELDERS (7): Pedro Ciriaco, Mauro Gomez, Jose Iglesias, Will Middlebrooks, David Ortiz, Dustin Pedroia, Jerry Sands.
OUTFIELDERS (5): Jacoby Ellsbury, Alex Hassan, Ryan Kalish, Daniel Nava, Ryan Sweeney.