The Japanese left-hander was hit by a line drive off the bat of Houston's Brian Hunter in the fourth inning.
Ishii, 29 on Monday, lay motionless on the field for nearly 10 minutes before his head and neck were immobilized by paramedics.
"The first thing that I saw was the blood, which scared me to death," Los Angeles manager Jim Tracy said.
"But fortunately, it was just a surface cut, not profuse and he never lost consciousness.
"I know he could hear voices and he told the trainers that his head hurt real bad. The fact that he was relaying those messages was a good sign."
Tracy confirmed however that Ishii is facing an "indefinite" spell on the sidelines as he recovers from the injury.
"He has a small skull fracture," Tracy added. "He had a CT scan and he will have one later this evening, but he is not in any type of danger.
"He is doing OK and has been stabilized. He will be out indefinitely, and what I mean by that is he will for certain not make his next start."
'Heads up'
Hunter, who hit the ball, admitted he was unsure whether to continue with his run after the the incident.
"As soon as I hit the ball, my natural reaction was to say 'heads up,'" said Hunter, who saw the ball hit Ishii on the left side of his forehead.
"I wanted to run out there and see if he was all right. You hate to see that happen.
"I'd rather hit into a double play than hit it like that. My thoughts and prayers are with him, his family and the Dodger organization."
Ishii took the loss in the game, allowing three runs and five hits in three-and-a-third innings before the injury.
It was his eighth loss in his last 11 decisions as his record fell to 14-10.