Jansen sprained his left knee in last week's 24-10 loss to the Baltimore Ravens. He took part in some drills on Thursday but was too sore to participate on Friday.
Jansen was one of three offensive linemen hurt against the Ravens. Left tackle Chris Samuels is out for the season with a torn right triceps, and backup Justin Geisinger is also done for the year with a knee injury.
Horton has not practiced all week because of a shoulder injury. Mike Green is expected to start at strong safety.
Coach Jim Zorn said he expects middle linebacker London Fletcher (foot) to play, while defensive tackle Cornelius Griffin (shoulder, abdomen) will be a game-time decision. Both did not practice Friday and were listed as questionable.
The Yankees made a late charge to beat out the Atlanta Braves for Burnett, who went 18-10 with a 4.07 ERA in 35 starts with Toronto this season. New York is still looking for one more starter, and Cashman left the winter meetings in Las Vegas this week to meet with long-time Yankee Andy Pettitte.
In December 2005, Braunecker and his agency, Frontline Sports Management, negotiated a five-year, $55 million deal that included an opt out clause after three seasons. It was the first opt-out provision ever in a pitcher's contract.
Between the money that Burnett earned in Toronto and the guaranteed $82.5 million that he's scheduled to receive from the Yankees, his overall payout from the 2005 Toronto contract will amount to $115.5 million over eight seasons.