Just days before Brandon Weeden's first start in 2015 as the Dallas Cowboys' quarterback, the team traded for veteran quarterback Matt Cassel. Weeden remains the starter for now, but if he continues to struggle like he did in the second half of Week 3, Cassel could emerge as the starter.

In Week 3, Cassel was behind quarterback Kellen Moore on the depth chart and he was inactive. Cassel's first task is to learn the Cowboys' offensive scheme and terminology under offensive coordinator Scott Linehan. He has had no issues with that so far.

"He's working hard at it," Garrett said Monday of Cassel, per Brandon George of the Dallas Morning News. "He's a smart guy. He's an experienced guy. It comes to him quickly."

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The Cowboys haven't made a decision yet on whether or not Cassel will be active in Week 4 as the backup quarterback to Weeden, but things are certainly trending in that direction.

"You ask him to call plays, 'Give me a play-call. What's the adjustment?' Garrett said. "Like you're a teacher. You're constantly asking him questions and you're trying to put him in situations as best you can to see what he knows. He did a lot of work with the two-minute stuff with the coaches last week during the defensive period. He can speak the language. He's getting more and more comfortable saying it. He's run a lot of these plays. He knows these concepts. As much as anything else, it's learning the terminology and learning the nuances of the system."

At no point in his career, starting for three different teams, has Cassel struggled to pick up the scheme.

However, Cassel's understanding of the scheme hasn't always led to success on the field. He has completed over 60 percent of his passes just twice over the last seven seasons, since he became a starter. He has also bounced around four rosters since emerging with the New England Patriots in 2008.