And what is he doing playing for the Patriots while wearing Mike Vrabel's old number?

For starters -- which, who knows, Ninkovich may be come Sunday at the Meadowlands against the Jets -- Ninkovich is no Vrabel, who was a defensive mainstay of the Patriots' three Super Bowl championship teams, as well as the 2007 AFC champions who went 16-0 in the regular season.

Here is Ninkovich's bio, courtesy of the Pats' media relations staff:

A veteran of three NFL seasons with the New Orleans Saints (2006, 2008) and Miami Dolphins (2007-8), he is originally a fifth-round draft pick of New Orleans out of Purdue. Ninkovich played in three games as a rookie with the Saints and then was claimed off waivers by Miami in 2007, playing in four games that season for the Dolphins. He began the 2008 season on the Miami practice squad before being signed to the 53-man roster in early November and playing as a reserve in one game. Ninkovich rejoined the Miami practice squad until being signed to the Saints' 53-man roster in early December. He was inactive for the final four games of the 2008 season for New Orleans. The Saints released him on July 30, 2009, and he was picked up by the Patriots on Aug. 2.

And there he was on the field Monday night against the Bills, seeing playing time after Jerod Mayo -- the Pats' leading tackler last year as a first-round draft choice -- went down in the first quarter with a knee injury.

Already, the Pats list two undrafted free agents, Pierre Woods and Gary Guyton, as starters at linebacker, now that Vrabel has been traded to Kansas City and Tedy Bruschi has retired. Eric Alexander, who also was undrafted, is listed as Mayo's backup on the depth chart

Outside linebackers Tully Banta-Cain and Derrick Burgess were used primarily as pass rushers, coming out of a three-point stance, against the Bills.

When the Pats were winning Lombardi trophies, they boasted a linebacking corps of Bruschi, Vrabel, Willie McGinest, and Roman Phifer. If it turns out Mayo will be out of the lineup for an extended period, then only Adalius Thomas is worthy of mention in the same breath with that bunch.

By the end of last season, the Patriots were so shorthanded at linebacker that they had to lure Junior Seau and Rosevelt Colvin out of retirement. It's hardly a reassuring situation for a team with Super Bowl aspirations, especially now that all-pro defensive lineman Richard Seymour has been traded to the Raiders for a first-round draft choice in 2011.

New England, sorry to say, has entered the Ninkovich Era.