The sequel will see Batman and Superman together for the first time on the big screen. Affleck will play Batman, while Henry Cavill will feature as Superman.
Freeman, 76, who as worked with Affleck in "The Sum of All Fears", is the latest celebrity to support him.
"It's a franchise! It'll stand on its own merits, and you can't really say anything until he's done it. The pre-judging was strange. Give him a shot!" Freeman said in a statement.
Meanwhile Freeman will be seen alongside stalwarts like Robert De Niro, Michael Douglas and Kevin Kline in buddy comedy "Last Vegas", which will hit the theaters Nov 22.