"Of course I'm protective of him, he's mine," the Master said, a possessive note in his voice. "And I'm not about to let you - any version, any regeneration - hurt him, again."
It didn't matter that this version probably never had, it was still a sore topic for him. And if the Doctor from his universe ever showed up, the one who'd left Jack behind, he'd probably... not be quite so polite at the first.