The 21-year-old spent July in London for Spain's unsuccessful Olympic campaign before joining his Old Trafford team-mates in Gothenburg for the club's friendly with Barcelona, and Carrick commended the goalkeeper on his performance.
"David just keeps getting better," he told MUTV.
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"We knew he would. The manager has shown great faith in him and he's getting stronger and stronger.
"His distribution is fantastic and he makes saves at good times. I'm sure he'll continue to do that."
Despite losing on penalties to Barcelona in a repeat of the 2009 and 2011 Champions League finals, Carrick was positive about the run-out.
The 31-year-old dropped into defence during the match but admitted he had no problem with the positional switch.
"It's happening a little bit more often these days," he added.
"It's the third time in pre-season now but it was a good work-out for us and a proper game against really good opposition.
"Forty-five minutes for me was good. I've had four games and now that half a game so it's lot of minutes under my belt.
"I'm feeling really good. There are still 10 days or so until the start of the season and that's enough time to shake things up a little bit more and sharpen up a bit so we'll be ready for the Everton game."
United kick off their campaign on August 20 away to the Toffees as they look to reclaim the Premier League trophy from neighbours Manchester City.