Not directly.
But once Duran gets the call, the Sox have enough people to cover 1b, including Dalbec, and three guys who might suddenly find out they have a lot less time in the OF in Santana, Hernandez, and Gonzalez. Thats an awful lot of bodies on the depth chart in front of Casas, and bringing up Duran just increases the availability of all those names for 1B.
I have serious doubts the Sox bring up Casas unless injuries make it a necessity.
Not to mention the whole issue of the 40 man roster. While we can easily dispatch Brewer or Brennan to accomodate the two players, it's not as easy of a decision for the team. The Sox are going to go through a lot of pitchers this year, and if they DFA two pitchers who make no money but have MLB experience, someone will claim them, giving the Sox that much less pitching depth. Most teams use at least 15 RP in a season. Do the Sox have that many RP ready for the team? And where do Brewer and Brennan fall on that list?
It seems to me this decision goes deeper than "Dalbec is struggling, just bring up Casas."...