The Portugal Under-21 international signed for United last month for a reported fee of £7.4m with manager Sir Alex Ferguson insisting that the winger has a bright future at the club.
The 20-year-old was named in United's squad despite initial reports he had not made the cut along with Owen Hargreaves.
However, UEFA confirmed that Bebe, who was playing in the Portuguese third tier last season, had been included and he could now make his Old Trafford bow against Rangers in the competition next Tuesday.
"I'm surprised by my inclusion in the Champions League squad," he said.
"It's a dream for me. I never thought I would have made it, but now I am a very happy man.
"I only hope that my confidence returns when I start playing some games and scoring goals, like I know how.
"At the moment I am working very hard each day in training.
"I intend to make the most of my chance and hopefully profit from the opportunity given to me."