United were held to a 0-0 draw at Old Trafford after managing just two shots on target against Eddie Howe's side.
Ronaldo, starting a league game for the first time since August, was substituted in the 72nd minute and was visibly disappointed with the decision as he walked off.
"We have to recover four games in 10 days and especially for the strikers, I want to keep them fresh," Ten Hag said.
"I want to keep them all fresh, we have to rotate because of some problems we have.
"We had to plan to cover for the four games because we want to win or at least get a result in all four games."
Pope began to take the kick himself, but Ronaldo, believing the ball was already live, nipped in before scoring into an empty net.
Ten Hag was involved in a heated discussion with referee Craig Pawson after the final whistle and suggested in his post-match news conference that Pawson had made a mistake.
"I don't have a comment, everyone has seen it," Ten Hag said. "Everyone has seen what happened today on the pitch, I don't have a comment."
After drawing a blank against Newcastle, United are now tied with Chelsea as the second-lowest scorers in the Premier League's top 10 (Bournemouth are lowest with 10 goals), but Ten Hag says he is not concerned.
"Our strikers will score, will score a lot, I'm confident about that, as long as we keep doing the work in and out of possession," he added.
"We score in almost every game. Today we didn't, but in the other games we score. It's clear it's about taking responsibility, I am convinced our strikers will take responsibility, but also other players, midfielders and defenders can also score goals."