Webb completed just 11 of 30 passes for 180 yards with one touchdown and one interception. The result was a season-ending loss to the Green Bay Packers.
Offensive coordinator Bill Musgrave said Cassel was brought in mostly because of his track record.
"He brings (us) some experience," Musgrave said . "He's a proven guy and he's (been helping) the quarterbacks through the offseason. He will help with his skills."
Cassel is still grappling a little bit with the new terminology of the Vikings but says he is becoming more accustomed to it.. A lot of the words are familiar but mean different things in this new offense so sometimes he has to remind himself what to do when a particular play is called.
"For me the important thing is just to keep progressing," he said. "I want to improve my reads and get my timing down with the receivers and try to help the offense finish drives. That's the same no matter if you're the starter or the backup or third-string."
Cassel's next game opportunity comes on Friday when the team travels to Buffalo to take on the Bills. Ponder is expected to take a few more snaps in that one but Cassel is likely to get plenty of playing time in the second and third quarters.
"(Matt) is still learning our offense," head coach Leslie Frazier said. "We just have to keep giving him opportunities and he will get better. There are some things we are doing here that he hasn't had to do somewhere else."