According to a tweet posted on Mike Salk of WEEI's Twitter acount (see below), Clay Buchholz was taken to Mass General Hospital while the rest of the team was in St. Louis. But Pete Abraham of the Boston Globe also tweeted out shortly after (again, see below) that Buchholz threw a session at Busch Stadium under the watchful eyes of manager John Farrell.
Clay Buchholz threw at Busch Stadium. John Farrell was watching intently.
— Pete Abraham (@PeteAbe) October 25, 2013
According to boston.com, there is no indication that Buchholz is going to sit out for game 4, when he is now scheduled to pitch.
Right now, there is no reason to believe that Buchholz will sit, but it may look something like what Joe Maddon pulled in game 4 of the ALDS.Currently, they have Felix Doubront and Ryan Dempster among the pitchers who could possibly give them multiple innings out of the bullpen if Buchholz is not 100%.