Look at his reference picture and then think of his arm's position, his neck isn't that free a target. Not to mention if Gigue gets into that position drawing a knife to strike seems like a massive waste of time, he could just punch Sigurd in the face in half the time and knock him out. Your character's strength is actually insane, giving him the benefit of the doubt in regards to his punching form he can generate more force with his punch than any living human at least twice over, Sigurd isn't a boxer (trained to take punches to the face) and even giving -him- the benefit of the doubt he'd still be debilitated by a single punch. Why waste time with drawing a knife?

That being said, Gigue is already an unstoppable badass, multiple rending wounds, badly injured arms and even broken ribs and he's still performing acrobatics and break dancing, what more can Sigurd do?