The Australian has been out of action since tearing the medial collateral ligament in his right knee in the Premier League defeat by Arsenal on December 8.
But the 28-year-old recently retrained training and potentially could feature against Everton, in Siewert’s first match in charge of the Terriers.
On whether Mooy could make his return, Siewert said: “I think so. But as you can imagine, I do not want to give me line-up now here. He is close and in training and I am glad to see him back on the pitch.”
Siewert did confirm that the home game with the Merseysiders comes too soon for Philip Billing, who has a knee injury.
Meanwhile, Siewert is staying tight-lipped on reports that Town are to sign highly-rated Charlton Athletic striker Karlan Grant for a £2m fee.
Grant has impressed in League One for the Addicks this season, scoring 14 goals in 28 league games and his form has brought him to the attention of several clubs in higher divisions.
Some reports have suggested that the player will undergo a medical today after a fee was agreed with Charlton.
Siewert said: “That is not my behaviour as I do not normally talk about players playing for other clubs. I just want to talk about the players who are in my squad.”