The 27-year-old has been the club's recognised No.2 for the majority of his four-year stay in England, but enjoyed an extended run in the side towards the end of last season while Shay Given was out injured.
The club's new boss Paul Lambert is eager to keep the USA international in his first-team plans after being impressed with what he has seen from him so far.
"I've watched Brad and some of his games when he was in the team last year and he was excellent," Lambert told the club's official website.
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"But when you come back at the start of the season nobody knows what's going to happen and it depends on whoever does well.
"Brad played very well the time he was in and maybe he found himself a bit unlucky to be back out.
"The club needs two or three good goalkeepers, so when Shay comes back from the Euros it will be a big bonus and we'll see what happens."
Guzan has only made eight league appearances in four seasons at the club, but seven of those came last season and he looks set to seriously challenge Given for a starting spot next season.