The Jaguars have yet to take their first regular-season snap, but they suffered a major setback with starting left tackle Cam Robinson ruled out Sunday against the Kansas City Chiefs because of a right knee injury.

Marrone said Robinson’s knee gave out after he was engaged in pass protection during a play in practice on Thursday.

Robinson tore the anterior cruciate ligament in his left knee last September during the opening home game against New England and spent nearly a year in rehab before practicing for the first time on Aug. 12.

Also, swing tackle Cedric Ogbuehi is listed as out for the opener because of a hamstring injury.

Already the Jaguars are down to their third left tackle -- Will Richardson. He worked mostly at right guard in the preseason and is expected to start in place of Robinson.

''You know what I've learned around here, I just take things day by day, and the guys that can play, play,'' Marrone said. ''And the guys that can't, they just tell me.''

The Jaguars listed Robinson as limited Wednesday, and he did not practice Thursday. On Sunday, the Jaguars will be facing a Chiefs team that finished with 52 sacks last season.

In addition, defensive tackle Marcell Dareus is listed as questionable to play Sunday with an elbow injury. And rookie tight end Josh Oliver, who missed all of the preseason with a hamstring injury, will not play against Chiefs.

Marrone stuck to a ''smarter approach'' plan throughout training camp and the preseason by limiting the amount of live tackling and not playing his starters in three of the four preseason games. The change was prompted by the amount of injures that occurred last season, especially on the offensive line, that led to a 5-11 season.

Last season, center Brandon Linder, left guard Andrew Norwell, right tackle Jermey Parnell and Robinson all ended the season on injured reserve, missing a combined 29 games. Four different players started at left tackle after Robinson suffered a season-ending injury in Week 2 against New England. And three different players started at right tackle during the final four weeks of the season.

Now it's paramount for rookie starting right tackle Jawaan Taylor and Richardson to void injury because it would force guard Brandon Thomas to become the team's fourth right tackle. Marrone didn't disclose much on Robinson's injury. He said Robinson had a MRI test done on his knee but didn't know the results.

Asked if there is a possibility Robinson could return in a couple of weeks or is a season-ending injury, Marrone said he's not a doctor, can't predict anything or has a clue.  

''Lets just take it one step at a time. Don't jinx us. We're down to a third [tackle],'' Marrone said.

Though Richardson, a second-year player,  worked some at left tackle during training camp before he was switched to right guard, he's played one snap at left guard since high school during a game — a kneel-down at North Carolina State. Richardson was working at left tackle when Robinson was injured and was told Friday morning that he's starting against the Chiefs.

''I haven’t gotten as much time [at left tackle] as I would like, of course. But at the same time, I’ve been playing tackle all my life,''said Richardson, who started at right tackle at North Carolina State. ''It’s just about taking the little things and taking them over to the left side.”

Richardson fell behind last season after suffering a shoulder injury in the preseason. Injury problems lingered into the regular season, and a knee problem forced him onto injured reserve in October. Richardson never played in a game last season as a rookie.