Allen had entered training camp looking to regain his starting job — remember that he has started all but one of the games he played since coming to the NFL as a first-round pick in 2001.
Even if that wasn't going to happen because of the promise shown by Smith and Davis last year, Allen nonetheless would play a key role as the team's nickel back.
Now, there's reason to worry that the knee will not hold up and that Allen might not be able to contribute much in 2010. Also keep in mind that he carries base salaries in excess of $5 million for each of the next two years, the last two on his contract.
With Allen currently sidelined, the Dolphins now are looking at Smith, Davis and a bunch of question marks.
Sure, Jason Allen has looked very good in camp, but the fact remains he hasn't produced on defense since coming to the Dolphins as a first-round pick in 2006.
Rookie Nolan Carroll has looked like a fifth-round steal many times in camp, but he's obviously comes up short with it comes to NFL experience and, like Smith and Davis last year, will go through some growing pains.
Veteran Evan Oglesby was placed on injured reserve on Thursday and Kevin Hobbs, who started two games for Detroit last year, was signed, but Hobbs is no lock to make the 53-man roster.
Former Ravens cornerback Frank Walker was in for a workout on Wednesday and there's a possibility he could sign at some point, but the reality is the Dolphins need to have Will Allen in the lineup to be as good in the secondary as they can be.
That's why this is such a worrisome development.