It doesn't appear that Guillon's surgery was too serious if the Reds think he can get some playing time in this season. Reds assistant GM Bob Miller had this to say about Guillon today:
11:13 am What's the status of LHP/1B Ismael Guillon? Is he expected to be ready for the GCL season?
11:14 am He had surgery in the off-season but hopefully he'll get a little action in the GCL or Dominican Summer League this year.