Porte ploughed off the road when descending at high speed with 35km of the 237.5km race remaining.
"I'm definitely out of the time trial," Porte said in a statement after being released from Vitoria Hospital in Barra.
"I won't be able to ride for at least 10 days, my arm's in a sling and I can't really move my arm."
Porte said he was lucky not to have been more seriously injured after a heavy impact as he came down the Vista Chinesa climb for the penultimate time and ended up in safety netting.
"We were away with a small group on the descent and on one of the corners I came around and there was a guy on the road who crashed and I had nowhere to go," Porte said.
"It was fortunate a tree stopped me from going over the side. I'm bruised and battered and sore and I'm disappointed but lucky I'm not worse off."
The same stretch of road also wrecked the gold medal hopes of Vincenzo Nibali later. The Italian broke both his collarbones after crashing on the final descent when leading.
Porte was considered a medal prospect for Wednesday's time trial.
(Editing by Peter Rutherford)
