From the official Opeth website:

Good news!

Lopez is feeling much better and will join the band in Seattle this Saturday!
Due to Lopez sickness Opeth were forced to cancel the gig in Edmonton. In Calgary and Vancouver Opeth played a reduced set.

The upcoming USA tour will feature support from American band Devil driver as well as Portuguese legends, Moonspell.

Martin Lopez is now in a much better state. As expected, the doctor's ordered a few weeks of relaxation due to overload of stress!

Band profile:

Opeth