IRVING, Texas -- All one needs to know about the 2014 Dallas Cowboys as they head into the Sept. 7 season opener against the San Francisco 49ers is that eternally optimistic owner Jerry Jones is headed into the season with tempered enthusiasm.

No longer is Jones pronouncing a Super Bowl or bust mantra for his downtrodden Cowboys, coming off four playoff less seasons and three 8-8 campaigns.

Instead he readily acknowledges a team in transition, one with their backs against the wall and facing an uphill battle for success in 2014 because of a lot of new faces and the lack of front line players on defense.

"These guys we're expecting to play have a lot to prove to play the way we expect them to play," Jones said. "I candidly have these thoughts that you do your best work when you have the longest odds.

"This team has no-name guys. Guys that weren't No.1 draft picks. Guys that were retired. You have guys coming back from injuries. This a to-prove group. The to-prove Cowboys."

The Cowboys should have one of the most explosive offenses in the league with quarterback Tony Romo, receiver Dez Bryant, running back DeMarco Murray and three first-round picks on the offensive line. But most games will end being shootouts because a Cowboys defense that finished last in the league in 2013, giving up the third most yards in NFL history, could be worse on paper in 2014.

Jones said the question marks on defense as well as the overall youth having him taking a different approach than in the past, thus lack of open optimism.

"When we had our initial team meeting in Oxnard, at training camp, we had 90 players there and I think 48 or 49 of the players had never been in that meeting," Jones said. "In other words, they were new players, over half of them. So I know they have been challenged and this is a pretty wide-eyed experience to come in, even if you're not a rookie. I know they were challenged.

"The good news is, they played to that, they practiced to that, they studied to that, and I think we can carry that into the first game against San Francisco, just the challenge. If you look at that schedule, they don't make them gimmes. I think we are challenged.

"We've got an offense that basically needs to execute, but that offense can be real good. The defense is a work in progress. And that's a challenge. I don't see that that means that we won't be successful at all. I just think there's probably more of a challenge than when you got DeMarcus Ware at one end and you got (Anthony) Spencer healthy at the other and you got all the guys in between, (Jason) Hatcher and the rest of them, or a healthy Sean Lee."

A lot of this was evident during a winless preseason -- the fifth in team history and the first since 2000 when Dave Campo directed the first of three 5-11 campaigns.

Preseason results don't matter.

But the bigger problem is that many of the guys Cowboys are counting on to help bolster defense didn't even get on the field in the preseason.

Defensive end DeMarcus Lawrence, picked in the second round to replace Ware as the primary pass rusher, will miss the six weeks of the season with a fractured foot.

Defensive end Anthony Spencer is still recovering from microfracture surgery and will miss the first two or three games and even though may never return to his Pro Bowl form.

Free agent signee Defensive tackle Henry Melton, a former Pro Bowler in Chicago, missed the preseason because of knee and groin issues and will be less than his best in the opener against the 49ers.

Defensive tackle Terrell McClain, another free agent signee, missed the entire preseason with an ankle injury and is questionable for the opener.

Defensive end George Selvie, the top returner pass rusher with seven sacks in 2013, should play in the opener but is hobbled by a shoulder injury that slowed him during the preseason.

And at linebacker the Cowboys are hoping that Rolando McClain, a former first round pick of the Raiders in 2011, can give them a spark after sitting out last season in semi-retirement.

Then there's a secondary that will be without cornerback Orlando Scandrick for the first four games because of an NFL suspension and will have hobbled cornerback Morris Claiborne on the field against the San Francisco after missing the entire preseason with knee and shoulder injuries.

Coach Jason Garrett said the team will be ready for the 49ers and whoever is available will play.

Garrett is 29-27 in 4 1/2 years as head coach. He is also in the final year of his contract. Even though the Cowboys remain a work in progress and a team in transition, Garrett said he preparing them to win.

"We started with a plan to make the team younger, to build the team the right way, to bring the cornerstone pieces in, and we feel like we've done that," Garrett said. "Now is that job complete? It's not even close to being complete. We understand that. But it's an ongoing process that you go through. It has a lot to do with the personnel. The guys you pick on draft day. The guys you bring in as free agents. You want to make sure you're doing it the right way, and we feel like we've done that and we'll continue to do that, and we feel like that's what gives you the best chance to have a good football team and a good season.

"Our objective is to win. There's no question about that. We take it one game at a time. We know what the challenge is. The 49ers are coming in here next week. They're a heck of a football team. They have a great program set up out there. They've got a lot of good players and good coaches. We're focused on that."

NOTES: DT Josh Brent is still awaiting word from the NFL on his reinstatement to the league and if he will be disciplined for any more games. Brent has not played since the December 2012 car accident that killed practice squad linebacker Jerry Brown. Brent was convicted of intoxication manslaughter and sentenced to 180 days in jail, with a judge allowing him to serve the final 45 days in an addiction rehabilitation center. The Cowboys will create a roster spot for Brent as soon as he's ruled eligible by the NFL. ... Owner Jerry Jones continues to maintain there was no wrong-doing or tampering in the late night conversation he had with Minnesota Vikings running back Adrian Peterson after the George Strait concert. Per a story in ESPN Magazine, Jones fielded a phone call from Peterson, who expressed interest in playing for the Cowboys. Peterson refuted that in a statement released by the Vikings.