The NCAA granted Keenum a sixth season of eligibility after he tore a knee ligament against UCLA in the third game of last season. Freshman David Piland was thrust into the starting role, and though he threw 14 interceptions, he finished with the league's third-highest passer rating (137.5).
Houston, in fact, ranked fifth in passing yards per game (334) and 11th in total offense (480.5 yards per game).
"There's a lot of people in the country who would take that tomorrow," said Sumlin, entering his fourth season in Houston.
But with Keenum running the show in 2009, the Cougars led the nation in total offense (563.4 yards per game), passing yards (433.7 per game) and scoring (42.1 points per game).
And even though Keenum hasn't taken a live snap in nearly a year, the league's coaches have already anointed him as Conference USA's preseason offensive player of the year. He has also been mentioned as a long-shot candidate for the Heisman Trophy, but he's hardly given a thought to any of that hype.
"I don't want to say it means nothing, because it's definitely an honor to be mentioned like that," he said. "But you just can't put too much stock in that, because you haven't played any football. You've got to forget what's happened in the past, and that's kind of all about what you've done in the past.
"Right now, we're all looking ahead," Keenum said. "We don't want to look in the rear-view mirror."
Keenum is within reach of several NCAA career passing records, and with top receivers Tyron Carrier and Patrick Edwards also back, there's no reason to think Keenum and the Cougars won't produce some monster numbers.
"Are we going to lead the country every year? Probably not," Sumlin said. "But I think we've proven that we'll be right around there with our trigger guy. Case just makes us better."
The Cougars lost six of their last nine games after Keenum went down in 2010, and finished 5-7. While Piland learned to run the offense on the fly, the defense also struggled, giving up 432.8 yards per game to rank eighth in the league.
Houston had moved from a 4-3 defensive alignment to a 3-4, and Sumlin acknowledged that the transition did not go as smoothly as he hoped it would. He hired a new defensive line coach (Carlton Hall) and linebackers coach (Jamie Bryant) and expects improvement from a unit that returns seven starters.
"With the guys that we have coming back and with the new additions, we have some work to do in the next couple of weeks," Sumlin said. "The good news is we have work to do with some really good players."
The top playmaker on defense last year was linebacker Sammy Brown, a junior college transfer who led Conference USA and ranked fifth nationally with 20 tackles for loss. The 6-foot-3, 240-pound Brown was on the list of honorable mentions by the league's coaches in 2010, and Sumlin says that snub is motivating him in early practices.
"He's playing with a chip on his shoulder," Sumlin said. "Last year, he was playing on talent. He wasn't in really ideal physical shape, but he had good numbers. Based on where he is right now, I think he feels like he's got something to prove."
Ironically, Keenum will make his return at home against UCLA on Sept. 3, the Cougars' season opener. Houston dodges 2010 conference champion UCF in the regular season, and has only one conference road game against a team that finished with a winning record last year -- the Nov. 25 finale at Tulsa.
High expectations are nothing new to Houston since Keenum took over the starting role during the 2007 season. Keenum says he and his teammates have learned to embrace them.
"Expectations are good, especially among the fan base," he said. "Just getting some buzz going around U of H football is always good. It's better to have people who care, then have people who don't care at all.
"As far as expectations for ourselves, we just have to expect to win every time we get on the field," he said. "Expect to be successful, expect to win. That keeps it really simple."