McCune could, Glenn could, Bonvillain could, Cotton maybe
Glenn is obviously stretched out and I'm including him as one of the top 3 starters when I mention the possibility of needing a 4th if the situation arises. There is no guarantee on the others. What are McCune and Cotton's longest outings of the year (not that Cotton would be considered as a starter anyway)? Bonvillain hasn't been stretched since he was moved out of the Sunday job. Isn't his longest outing over the last couple of months only about 3+?
Again, I'm not saying we would have no hope of getting by in a pinch. I'm saying we wouldn't be able to handle it without either asking someone to perform in a role they haven't been asked to previously, without extending the bullpen and thereby affecting their availability the rest of the series/tournament, or both.