The 31-year-old believes his team-mate will be unperturbed by the prospect of returning to face his former club on Tuesday, and says Madrid do not depend solely on Ronaldo
The 28-year-old heads to Old Trafford for the first time following his €92 million move to the Spanish capital in 2009 but, despite earning legendary status with the Premier League giants, Alonso believes Ronaldo will put emotions to one side and focus his efforts on eliminating his former team.
"Cristiano Ronaldo will get a positive reception, but when the match starts, he will forget everything and this won't affect his performance, as ever," he told Uefa.com
"It is sometimes different when you face your former team, but for us he is decisive and he will do his best tomorrow."
The World Cup winner also played down the importance of Ronaldo's individual performance ahead of Tuesday's clash, insisting the Spanish giants have other means of securing victory.
"If Cristiano plays good, we will have more chances, but we can lose with him in the team, too," he added. "The team isn't just about Cristiano. Other players can have an impact, too."