After Tyler Lyons struggled in his last start, many were quick to speculate that the Cardinals might make a change in the rotation again, perhaps even bringing Michael Wacha back. However, the way they are handling their starting pitchers down at AAA Memphis tells a different story.
As reported by Derrick Goold, the Cardinals are shifting to a modified 6-man rotation down at Memphis to help monitor the innings for Wacha. In the meantime, the Cardinals other top prospect, Carlos Martinez, will stay on his normal 5 day rotation, to build up stamina to be ready in case he's needed at the major league level at the end of June.
Thus, its pretty obvious that, should Lyons falter, Martinez would be the next in line for the 5th starter spot.
The Cardinals have already done their part to keep Martinez' innings down by using him in the major league bullpen for a month. Plus, his visa delay at the start of the season also worked in his favor. Thus, between the majors and minors, Martinez has only logged 41.2 innings so far, compared to 75.1 innings for Wacha.
If Martinez were to be called up at the beginning of July, the Cardinals would have about 81 games left, which would give him about 16 starts with the club (plus, maybe another 2-3 starts at Memphis). Assuming 6 innings per start, that would be 114 innings and, combined with his innings to date, would put him at 155.2 IP. If we assume that Martinez is on the same 150 innings limit as Wacha, then that would be a reasonable innings total.
Based on that, it appears that Martinez is being prepared to take over the starting role at the end of June and for the rest of the season, if necessary, and Wacha is now out of the picture.
As for Wacha, I could see him getting another 10 or so starts at Memphis and then being called up in September to work out of the pen for the Cards. This would be the ideal situation for him and could provide a boost to the Cardinals beleaguered pen down the stretch.