The Portuguese's future has been a constant point of speculation over the past few weeks amid his desire to play Champions League football.
Despite this, Ten Hag has constantly mentioned that the club want to keep him, and he is delighted to have the 37-year-old for the Brighton game.
He said: "I'm really happy. We have a top striker and I'm really happy he's here, he's in the squad [ Brighton game] and we stick to the plan."
United have suffered a blow in the lead-up to the Premier League opener on Sunday afternoon with Anthony Martial suffering a hamstring issue.
The Frenchman was expected to lead the line against the Seagulls, but he could now be sidelined for a short period of time with the setback.
In his absence, Ronaldo could lead the club's attack. Ten Hag has refused to confirm whether the Portuguese will start up front on Sunday.