Raul, 33, has proved he is still capable of delivering at the top level in recent weeks with three goals in his last four games, including strikes in both legs in the quarter-final victory over Inter.
Metzelder has now revealed that, when Raul decided to end his long association with Madrid last summer, he also had the option to move to Old Trafford or the MLS.
"They tried to sign him this season," Metzelder, who also left Madrid for Schalke last summer, told the Daily Mail. "He talked to me about it. I don't know if he thought about it.
"A player like him has offers - from clubs in the United States, England but also Schalke. I tried to convince him. He got to know Germany in the 2006 World Cup and knows the atmosphere, the stadiums, the infrastructure.
"I said to him, 'You have to experience it'. He's a big player and his influence is great."
Schalke's victory over Inter means they will play United in the semi-finals for the chance to reach Wembley to take on either Barcelona or Real Madrid.
"This is a big day for us, the only German club to be left in the Champions League, with three of the biggest clubs in the world," Metzelder added. "It's only Raul who has played finals - the rest of us just watch them on television."