Sir Alex hailed Ronaldo's leveller and realises he will be a big threat again in the return leg.
"What a header," he exclaimed. "Unbelievable. You can't stop that, I've got to say, with that leap and spring and he holds himself in the air. And the power in the header. I came in at half-time and said: 'Patrice did you not challenge for it' but I've seen the video.
"I thought we did well and it was difficult for Cristiano playing against us, his old team. Maybe there was a little bit of emotion attached to it but he was still a big threat for them.
"It's very open. I think they'll score at Old Trafford. We know they're going to be a tremendous counter-attacking team because we've seen it when they played Manchester City at the Etihad. They absolutely dominated the game in the first half.
"So we've got a big job on our hands but it's definitely within our grasp, no doubt."