Leary has been bothered by back soreness for the last few days.
The MRI will be used to diagnose exactly what is wrong with him and how much time he will miss. The Cowboys do not believe it is anything serious and that Leary should be back by this preseason game if not the next. But what this does do is allow La'El Collins an opportunity to take the starting job from Leary. Leary was going to walk into week 1 as the starter and unless there is some significant injury this battle will likely rage on.
Collins is a rookie after all but he dominated the Charger's defensive line. Ever since Collins was drafted there has been speculation of when he will take over a starting position. This is his chance to become a day 1 starter by playing healthier and being younger than his counterpart Leary.
Collins will be running with the first team in joint practices this week against the Rams which should provide plenty of valuable experience for the rookie. The Rams have one of the best defensive lines in the NFL so it should help Collins early on to get some competition with the best of the best.