Villa were poised to secure the 23-year-old last week after beating a number of clubs to his signature.
However, the 2007 MLS Goalkeeper of the Year was denied a work permit by the Home Office.
"We wanted to try and get Brad Guzan in because I believe he has got really good ability," he told the Birmingham Mail.
"He wanted to come to Aston Villa, which was really encouraging, but his appeal for a work permit was turned down.
"They do not tell you why; six people sit in on it and take a vote. I am certainly going to have as look at it again in the future.
"If you are talking about the keepers that America has produced then he is in line with those."