The San Francisco 49ers have been to three straight NFC title games and the expectation is to take the next step and finally win it all under coach Jim Harbaugh.

The Dallas Cowboys have finished 8-8 in three straight seasons, and it could be an accomplishment to reach that mark in 2014.

Neither of these franchises have been strangers to controversy over the years, and the 49ers head into Sunday's opener at Dallas with the status of defensive tackle Ray McDonald in serious doubt for a unit that is already short-handed.

The build-up to the season took a difficult turn for San Francisco last Friday when star linebacker Aldon Smith was suspended for nine games for what the NFL called violations of the league's substance abuse and personal conduct policies. The defense is already without linebacker NaVorro Bowman, who is on the physically unable to perform list due to a gruesome torn left ACL suffered in last season's NFC championship game loss at Seattle.

The news got worse for the 49ers this past Sunday when McDonald was arrested on felony domestic violence charges. It came only days after Commissioner Roger Goodell cracked down on such offenses with far harsher penalties than the two-game ban he gave to Baltimore running back Ray Rice.

The 49ers have not ruled McDonald out this weekend. Harbaugh said the decision "will be based on information and facts," and Goodell said Wednesday that the NFL is closely watching the case.

"There's two very strong principles in play. No. 1 is we will not tolerate domestic violence. The second principle is the respect for due process," Harbaugh said. "It's something we all know, we all live in America, and we all understand that sometimes patience is required when it comes to due process. ... You're innocent until proven guilty."

General manager Trent Baalke and Harbaugh have spent recent days denouncing such behavior and reiterating their stand for zero tolerance when it comes to domestic violence.

Asked about the 49ers having players arrested an NFL-high 10 times since 2012, Harbaugh said Tuesday that the team is doing "everything in our power to make sure there isn't a pattern forming."

San Francisco has won at least 11 games in each of the last three seasons, going 12-4 last year before winning twice in the postseason and then losing 23-17 to the NFC West rival Seahawks.

The 49ers have averaged 32.3 points in winning all three season openers under Harbaugh, and offensive success can be expected Sunday unless the Cowboys improve their woeful defense from last season.

Dallas allowed a league-worst 415.3 yards per game for the NFL's third-worst mark since the merger in 1970. The franchise's all-time leader in sacks, DeMarcus Ware, has left for Denver while Jason Hatcher, who had a team-high 11 sacks in 2013, is now with Washington.

In addition, rookie defensive end Demarcus Lawrence will miss at least half the season after the second-round pick was placed on the short-term injured list because of a broken right foot.

The Cowboys turned in a winless preseason and even normally confident owner Jerry Jones doesn't sound too thrilled about this year's club.

"I think there is a difference being optimistic and assessing the odds," Jones said. "You've got guys out there, no-name guys. You've got guys out there who retired. You've got guys who are coming back from injury. Man, this is a `to prove' group."

The offense will again revolve around Tony Romo, who was fifth in the NFL in touchdown passes with 31 a year ago but enters his 11th season after back surgery. Romo insists he won't alter how he plays.

"You'd be selling the game short if you think you could control all parts of the game," Romo said. "It's a very physical, fast-flowing game that has humbled the best players who have ever played. There's only one way to play it -- all out, all the time."

No team has ever finished 8-8 in four straight years. Dallas entered Week 17 in each of the last three seasons with an 8-7 mark in a winner-take-all contest to capture the NFC East and has fallen to the Giants, Washington and Philadelphia last year. An injured Romo missed the 24-22 defeat to the Eagles.

This marks the second straight year in which Colin Kaepernick begins the season as San Francisco's starting quarterback. He had 21 touchdown passes and four on the ground last year while his 58.4 completion percentage ranked 31st.

The 49ers were third in the NFL in rushing with 137.6 yards per game. Frank Gore was ninth in the league with 1,128 yards as he topped 1,000 for the seventh time in eight seasons.

Romo is 2-0 as a starter against San Francisco with 686 passing yards, five TDs and no interceptions. He played through a broken rib in a 27-24 overtime victory in the last meeting Sept. 18, 2011.

His major target at receiver is Dez Bryant, who finished third in the NFL with 13 TD receptions and had 1,233 yards last season.