Keane spent last season on-loan at Leicester City.
"Sometimes it is difficult to judge centre-halves over just one or two games because they can only play as well as the strikers they're up against. If they don't have too much to do it's difficult to see how good they can be," Berg told the Manchester Evening News when discussing Keane's performance in the U21 final against Tottenham.
"Keane was given a stern test, though, and handled himself very well.
"They were playing against decent strikers. Harry Kane in particular is a very good player."