Speculation has been rife about Ronaldo's future at United following a trophy-less campaign and their failure to qualify for the Champions League this season.
"What I know about him is he did a fantastic job for Ajax (Amsterdam), that he's an experienced coach," Ronaldo told the club website on Friday. "But we need to give him time. Things need to change the way he wants."
The 37-year-old has been among the few bright sparks for United in an otherwise dreadful season under interim boss Ralf Rangnick, scoring 24 times in all competitions.
"I hope we have success, of course, because, if you have success, all of Manchester is going to have success as well. I wish him the best," added the Portuguese.
"We are happy and excited, not only as players, but the supporters as well," Ronaldo said. "Let's believe that next year we are going to win trophies."
Ten Hag, who has signed a three-year contract, comes to United after five seasons at Ajax, where he led the side to three league titles and two Dutch Cup triumphs.
United, sixth in the league, travel to Crystal Palace for the final game of the season on May 22.