Executive producer Hart Hanson jokingly implied that swine flu was to blame for the 40-year-old Boreanaz's absence. "First time in Bones history we are shut down from production," Hanson tweeted. "Damn swine flu! That's gonna cut into Christmas hiatus."
Boreanaz called in sick on Monday, but with nothing more than a seasonal flu, a studio rep tells TVGuide.com.
"We expect him back tomorrow," Hanson later tweeted.