De Gea, who joined United for £18 million in the summer, came in for criticism earlier in the season after a series of shaky displays.
The Spaniard was at fault for two of the goals that saw Blackburn win 3-2 at Old Trafford on New Year's Eve, but ahead of United's trip to Ewood Park on Monday, Ferguson believes De Gea, who has kept three consecutive clean sheets, is no longer a weak link in the side.
"He got a grip of the situation," Ferguson said. "He did not let the mistakes get to him and now he is playing with confidence which is a great factor for any goalkeeper.
"The area where he has been criticised has been in dealing with aerial balls into the box. That last corner kick Blackburn had at Old Trafford, he should have dealt with that better. He knew that at the time and it is a situation he has addressed.
"He stood up to the situation; he knew it was a challenge. It took him time to adjust to the different ways of the English game and it showed. But the other night, he produced one or two terrific punches when Fulham put the ball in the box at the start of the second half. We knew he had the ability and this is what we have seen."