I think that Lopez should not be too much of a problem for Andy. My principle concern is the strong possibility that Andy may be opposed by Donald Young.
Having watched Young's impessed defeat of Wawrinka. With Andy knowing that he has already lost to Young very badly, I believe that AM will have to change his game plan to overcome Young if he has to meet him in the round after Lopez. Young is a vey strong young man and an accurate base-liner. Long rallies suits Young very well as do drop shots. Coupled with the rather vociferous US supporters, which will almost certainly get up Andy's nose.
It's up to Andy but he can overcome Young as long as can maintain his level of concentration at a high level.
Incidentally, if the match-up is to between AM and DY, I am certain that it will be a late night performance, ie. early Monday morning.
OSS, when Andy lost to Donald, he was in a bad place mentally and never really turned up for the match, Donald did not so much as win the match, more like Andy handed it to him! However, that said Donald has to overcome The Whiley Chela first.