Bergstrom made two crucial saves at important timesin Saturday’s 3-0 League One win over Morecambe at the Weston Homes Stadium.
The 19 year-old is on loan from Premier League Chelsea.
"Lucas is a top young goalkeeper who is only going to get better,” McCann said.
"I feel lucky to have two of the best young goalkeepers in the country at the club in Lucasand Harvey Cartwright.
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"Lucas made a big save from Cole Stockton in the first-half at 1-0 and another save at 2-0 which was important.”
Cartwright has a thigh problem and has missed the first two League One matches of the season. Young Will Lakin sat on the bench on Saturday in place of Will Blackmore.
Midfielder Jeando Fuchs was the only Posh substitute apart from Lakin not to get on and McCann revealed after the game the Cameroon international is suffering from an unspecified minor injury.
McCann also disclosed teenage striker Ricky-Jade Jones was left out of the matchday squad for tactical reasons. Fellow speedy forward Joe Taylor was preferred and he did well after coming on late in the game.