I don't think Juanma looked tired at all against Penalosa. With Mtwaga he did seem tired, but I read he said he has heard that a lot, but that it's not the case. He says he wasn't tired, but that he was genuinely hurt and was just surviving.
By round 6 it was evident that he slowed down. If he said it, then wow! Maybe he suffered some damage in that tough fight. I hope its not a mistake taking this fight too soon.
His stamina is VERY good, you just cant throw 100 power punches a round and expect to be fresh come the championship rounds.