Per the beat reporters, either Ross Wolf or Neil Ramirez will make Darvish's scheduled start tomorrow.
The indications are that this isn't serious, with T.R. Sullivan describing it as a "fatigue" issue, and the beats are saying on Twitter it is expected he will be able to be activated on July 22, the first day he would be eligible to return.
Still...this sucks. No word yet on a corresponding roster move.