De Gea produced a series of excellent saves at Fulham on Saturday as United eked out a crucial 1-0 win.
And match-winner Rooney was quick to highlight the Spaniard's contribution.
"David has made some great saves over the last few weeks," the England frontman said.
"I know he got a little bit of criticism after the Tottenham game but it wasn't the biggest mistake I've ever seen.
"We're all behind him. He's a great player for the future as well."