Now, their teams will square off for the first time since Cassel has joined the Chiefs.
It's a shame that Brady's former understudy won't be able to play against him on "Monday Night Football" because of a hand injury that he suffered in his team's last game.
At any rate, here is the tale of the tape between Brady and Cassel.
Cassel has been known to get "happy feet" while he is in the pocket at times.
Usually when a pocket collapses around him, he doesn't always step into it and has to either run for his life or he gets sacked.
When you look at Brady's pocket presence, you would see that he is one of the best in the league in this area.
Like Ben Roethlisberger, he somehow finds a way to get the ball to his receivers in even the most difficult of times.
Cassel is average to below average in the overall accuracy department.
He's not the best at throwing in the run, and tends to throw both behind and in front of his targets on a regular basis.
Brady's accuracy is one of his great strengths.
Not only he has had a career completion percentage of nearly 5 percent better than his understudy, but he has also been one of the most accurate QBs in the league over the past five seasons.
This could be one of Cassel's biggest assets that he provides the Chiefs at QB.
Although not the most mobile quarterback in the world, he has rushed for over 700 yards in his NFL career.
Compare that to Brady's 600-plus rushing yards in five more seasons of play, and you will see that Cassel is indeed the better runner of the pair.
Cassel also has a career YPC average of 3.7, while Brady has averaged about 1.8 yards every time that he carries the ball.
This comparison isn't even close.
Matt Cassel will often go to his first read, while Brady tends to pass to his second and even third read at times.
Also, Brady is much better at using audibles at the line of scrimmage and pointing out what a defense might be doing.
His understudy is still learning how to improve in both of these areas.
Brady and Cassel both have great size for a starting NFL quarterback.
Tom Brady is 6'4" and 225 lbs, while Cassel checks in at 6'4" and a little heavier at 230 lbs.
Both players are not extremely mobile, but both are athletic at the QB position.
This one is too close to call.
Cassel actually has one of the worst deep balls in the entire league out of starting QBs.
It's been so bad at times that Chiefs receivers have had to knock the ball out of defenders' hands on several occasions because they were in better position to make the catch.
On the other hand, Tom Brady doesn't have one of the best deep balls either.
However, it is still much more accurate overall throwing it long, just ask his former teammate Randy Moss.
Both Brady and Cassel are known for being good leaders on and off the field.
Cassel has not only taken control of his offense, but he has also had other offensive players come over to his house to help learn the playbook better during the recent NFL lockout.
Brady has been the leader of the Pats offense ever since he stepped onto the field for the first time in 2001.
I see both of these guys being neck and neck in this area.
Cassel has the ability at times, but is not very consistent in this role.
As a QB, he has been labeled as more of a game manager rather than a game-changer for KC.
On the other side, this is what Tom Brady has become known for over the years.
If it wasn't for his ability to take over games, the Pats would have likely not won three straight Super Bowl back in the early 2000's.
There you have it, Tom Brady won in five categories and Matt Cassel won one of them.
Overall, I think it's clear that Brady is and will always be a better QB than this understudy Cassel.
He has more talent, much better attributes and an uncanny way to put the Patriots on his shoulders at times.
Brady will likely end up in the Hall of Fame someday as one of the best QBs of all time.
Meanwhile, the best that Cassel could do is become one of the better Chiefs quarterbacks in their franchise history.
Brady is better than Cassel, and it is a unanimous decision.