Seven minutes into first half stoppage time, Junior Hoilett dispossessed Ridgewell and raced clear to round Ben Foster and slot home to cancel out Lee Bowyer`s 32nd minute opener for Blues at Ewood Park.
"We can't afford to give those sorts of gifts away but we came back in the second half," said McLeish.
"We really could have crumbled after that when we had our backs to the wall.
"It was a bad moment for the player (Ridgewell) but the next challenge for him was to see if he could recover from it and that's what he did.
The Blues boss added: "In the end I'm happy with the point.
"Seb Larsson's free-kick crashed off the post but you can never rule Blackburn out with their long throws and some excellent footballers."