The 23-year-old Dutch international has arrived from France on loan until the end of the season and made his Town debut in the FA Cup victory over Bolton Wanderers.
“It is absolutely up to us,” said Wagner, who is all set to complete the signing of £10m midfielder Alex Pritchard from Norwich City.
“Even if every club who loans a player – and we do as well – has the expectation they will play, because if not it makes no sense to make the loan, the decision is absolutely up to us.
“The player, first and foremost, has to perform, obviously, but then it is up to us.”
So does Kongolo provide the competition and flexibility which Wagner wants among his defensive selections?
“Yes, especially with Terence, who is a left-footed centre half who can also play left back,” said Wagner.
“It is something we’ve been able to bring into the group which we haven’t had before and it gives us more options, absolutely.
“He has had a small winter break, even if it’s not so long, and he needs more minutes in training so that he can be at his best.
“But we are happy he is in the group, and we will need all our players over the rest of the season.”
Will Kongolo play against West Ham United?
“He is in the competition for a squad place and for the starting XI,” confirmed Wagner.
On Collin Quaner, the boss added: “His injury is not as serious as we first thought at the beginning, but at this time he is not right.
“He will be ready next week for training and preparation for the Stoke City – that’s how it looks.”