The Real Madrid attacker had the chance to secure the three points for the Seleccao when his side were awarded a spot kick in the 79th minute.
However, the 31-year-old smacked the post with his effort and suffered further woe later on when he had a goal disallowed for offside.
But Alaba says there was only one word going through his mind when he saw the three-time Ballon d'Or winner prepare to take the penalty.
When asked on German television what went through his mind as Ronaldo stepped up, the Bayern Munich left-back chose to give his answer in English, saying: "F**k."
The 23-year-old admitted that his side were lucky to get a draw against Portugal, who hit 23 shots in the game, with 20 coming from Ronaldo, but believes his side can put on a good display in their last game group with Iceland.
"It's not a bad result," he said. "We were very lucky because they missed the penalty. We're glad we got a point from this game.
"We know it will not be an easy game against Iceland. They are a great team, as we saw in the previous game against Portugal, but we know what we are worth and we will do everything we can to win."