Dallas Cowboys linebacker Rolando McClain has been suspended for the first four games of the 2015 season after violating the NFL substance-abuse policy, the league announced on Thursday.

"I apologize to my family, the Cowboys organization, my teammates and Cowboys fans for my mistakes," McClain said in a statement. "I will not break the rules of my profession in the future and I regret my error. I look forward to returning to the field in Week 5, when I hope to help my team beat the Patriots."

McClain's suspension means that Cowboys will be without both McClain and Greg Hardy for the first four games of the season. Hardy was hit with a 10-game suspension back in April, although that suspension was appealed and could end up being reduced. 

Here's three thing to know about McClain's suspension. 

1. McClain will miss four games. McClain's suspension means the Cowboys won't have their second-leading tackler from 2014 for the first four games of 2015. McClain started in 12 games and tallied 81 tackles for the Cowboys last season and his skills will be sorely missed, especially when Dallas travels to Philadelphia in Week 2. 

Besides the Eagles game, McClain will also miss the regular season opener against the Giants, along with the Cowboys' Week 3 game against Atlanta and the team's Week 4 game at New Orleans. 

Despite the suspension, McClain is still allowed to participate in all of Dallas' preseason practices and games. After the suspension kicks in, McClain will be eligible to return on Oct. 5. 

2. McClain was already facing a suspension. The Cowboys have known since at least February that McClain might be suspended. At the time, McClain was a free agent, but Dallas chose to re-sign him to a one-year deal anyway, even though the team knew a suspension was very possible. 

McClain's latest suspension definitely isn't the first time he's run into problems since being drafted in 2010.  The Cowboys linebacker has been on thin ice almost since the day he was selected No. 8 overall by the Raiders.  

Since 2010, McClain has retired twice and been arrested three times. McClain's most recent retirement came in April 2014 when he was with the Ravens.

After things didn't work out in Baltimore, the Ravens traded McClain to Dallas in July 2014 and McClain ended up having a resurgent season with the Cowboys. 

The Cowboys knew McClain was a risk, which is why the team only signed him to a one-year, incentive-laden deal in April. 

3. Who will fill-in for McClain? Although McClain was arguably the best linebacker the Cowboys had in 2014, his suspension shouldn't cause anyone in Dallas to panic. The Cowboys signed veteran linebacker Jasper Brinkley in March and there's a good chance that Brinkley will be the guy who fills-in for McClain. 

Brinkley has started 29 games over the past three seasons while playing for both the Vikings (2012, 2014) and Cardinals (2013). 

The Cowboys also have second-year linebacker Anthony Hitchens. The 2014 fourth-round pick could end up as the starting middle linebacker during McClain's suspension. Hitchens started 11 games for the Cowboys in 2014 and played pretty much wherever the team asked him to play. 

Rolando McClain has to sit out the first four games of the  2015 season. (USATSI)
Rolando McClain has to sit out the first four games of the 2015 season. (USATSI)