Coach Tony Sparano refused to disclose specifics on why Allen, who had started all 43 games he spent with the Dolphins over the past four years, was placed on IR. The move was among a flurry of activity for the Dolphins over the weekend.
"I'm not going to get into the specific reason why we did any of these things," Sparano said, "but I just think that it's something that had to be done right now."
Among the Dolphins' other moves Sunday they terminated the contracts of defensive ends Charles Grant and Marques Douglas and guard Cory Procter. Miami also was awarded four players off waivers -- rookie defensive ends Clifton Geathers and Robert Rose, and offensive linemen Jermey Parnell and Joe Reitz.
The Dolphins, who were 7-9 last season, now have 20 players who are either rookies, first- or second-year players. They have 23 players who are five-year veterans or older.
Miami expects to start three rookies (defensive tackle Jared Odrick, right guard John Jerry and strongside linebacker Koa Misi) and four second-year players (cornerbacks Vontae Davis and Sean Smith, free safety Chris Clemons, and wide receiver Brian Hartline).
Allen's veteran wisdom could have helped the young secondary and during training camp rookie cornerback Nolan Carroll, a leading candidate to start at nickel defensive backs, mentioned more than once how it was comforting to be able to pick Allen's brain.
"We're trying to develop some young players and you have some of the young players you have developed in that mix and then you have a good group of veteran players," Sparano said.