Ronaldo is a free agent after he mutually agreed to terminate his contract with United in November following a controversial interview before the World Cup.
The 37-year-old said he felt "betrayed" by the club for the way he was treated and added that he didn't respect Ten Hag.
When asked about Ronaldo's exit for the first time, Ten Hag told the club's official website: "He's gone and it's the past. We are now looking forward and we're looking to the future."
Sources have told ESPN that Ronaldo is fully focused on the World Cup in Qatar and will make a decision regarding his future after the tournament.
Ten Hag added that he is happy with the signings made during the summer transfer window.
"We looked and with football players clearly that is the first thing, the capabilities a player has," he added. "The human being behind is also an important factor, but you can't underestimate that.
"You need the right characters in your dressing room, not only if you want to win a game but if you want to win trophies."
United return to action on Dec. 21 for a Carabao Cup round-of-16 clash against Burnley. Ten Hag said he is confident his players will be ready to compete after the World Cup.
"We had a plan, we have prepared the players with what the plan is so there can't be any confusion about what the programme is," he said. "We make the players aware of the fact that, after you are out of the World Cup, you have to return to the club and the league immediately goes on.
"You have to be ready for that, but I think our players are used to it. Our players are winners, and they are battling now for the World Cup, and in the moment they are out -- hopefully one is the winner -- they have to deal with that. With the success they have, or the defeats, they have to deal with it and of course they have to be ready for another challenge."