After getting cut in spring training, Cassel was re-signed two days later and began the year in Triple-A Portland. In 18 games, including 11 starts, he went 3-5 with a 6.48 ERA. In 76.1 innings he allowed 96 hits, walked 28 and struck out 44. He gave up 12 homers and the opposition hit .306 off him. He was demoted to Double-A on June 30.

Cassel went 6-3 with a 2.29 ERA over 12 starts for the Mobile Baybears, allowing two runs or less in nine of his starts. In 78.2 innings he allowed 66 hits, walked 18 and struck out 75. The opposition hit .224 off him and he allowed three homers.

2005

Cassel went 3-3 with a 3.35 ERA in 24 games for the Mobile BayBears, including three starts. In 43 innings he allowed 45 hits, walked 16 and struck out 29.

Cassel went 3-2 with a 4.62 ERA in 23 games for the Portland Beavers, including three starts. In 39 innings he allowed 54 hits, walked 17 and struck out 21.

2004

Cassel went 4-2 with a 3.74 ERA for Mobile in 2004. In 74.2 innings of work he allowed 76 hits and walked 27.

Cassel is famous for not allowing a homer over a span of 160 innings between 2002 and 2003 with Fort Wayne and Lake Elsinore.