De Gea – regarded as the one of the best keepers in the world – produced another stellar performance as United defeated Watford 2-1 in the Premier League on Saturday.
The Spain international, who was criticised for his displays at the World Cup, made a stunning save to deny Christian Kabasele at the death, having earlier thwarted Troy Deeney.
Former United keeper Foster, who left Old Trafford in 2010, likened De Gea to Barcelona superstar and five-time Ballon d'Or winner Messi.
"He is the Messi of goalkeeping. He has been the best goalkeeper in the world for years," Foster said. "He is absolutely brilliant now. Some of the saves he makes at really critical times are just breathtaking.
"He does it all the time. It's almost like he is not even bothered either! It would be so nice to pull those saves off, get up and it's almost like he just wants to go home. He can't be bothered!
"But seriously, he is brilliant. A top goalie and if any young goalie out there wants to learn how to be a goalkeeper watch David De Gea. He is world class.
"I think the thing with David is that because he is so natural, from what I hear as well he is not a great trainer. Training doesn't do it for him.
"But three o'clock, the adrenaline rush and what comes with that is what turns him on. I think that's something that you can't really teach. He's got the game management, the game nous of what to do at any given time and when it happens."