Lionel Messi’s disgust for Major League Soccer's new injury rule is one thing. How he openly criticized the rule is quite eye-opening.

Messi waited impatiently on the sidelines, eager to return to action before halftime last Saturday against CF Montreal, after being treated on the field for a left leg injury.

Messi looked directly toward a camera and sent a message to MLS: This sitting-out-two-minutes-before-returning injury rule needs some work.

"With these type of rules," Messi said as he shook his head.

The second part of Messi’s statement was hard to decipher: It’s going bad? We are doing badly? We’re going in a bad direction?

It wasn’t positive, or in favor of the rule, that’s for sure.

Messi finds himself in a camera’s view of so many adoring fans on a day-to-day basis. He humbly greets them with a smile, a wave, sometimes a hug for a young fan who steals one, and mostly never uttering a word during viral interactions.

But in this moment Messi sought out the camera, looked right into it, and voiced his disapproval directly to MLS.

You know this rule needs some work when the greatest player in the world, who rarely voices his opinion, feels audacious enough to openly share his displeasure.

MLS has not yet responded to a request by USA TODAY Sports on Monday for further comment on Messi’s opposition.

Why does Messi, Inter Miami feel slighted by injury rule?                           

Messi and Inter Miami have reason to gripe about the rule and an inherit flaw they encountered: They essentially felt penalized at a 10-v-11 disadvantage in this instance.

Messi received medical treatment on his legendary left leg after being tackled by Montreal’s George Campbell, who did not receive a yellow card for the sequence.

While Messi was ready to return to action, after walking to the sideline on his own to observe the two-minute wait, the situation left Inter Miami down a man on the field.

"With this rule change, there are situations that need to be reviewed," Inter Miami coach Tata Martino said after the game. "For me, the infraction (by Campbell) was clear. It was a yellow card and, in the end, we were the ones who lost Leo for two minutes."

Inter Miami needed newcomer Matias Rojas to line up for a free kick – a kick Messi would have taken had he not been sidelined. Luckily, Rojas' kick was an impressive goal score, and sparked the club’s 3-2 comeback win.

What is the MLS off-field treatment rule?

The MLS new off-field treatment rule states: If an injured player remains on the ground for more than 15 seconds and the medical staff enters the field of play, the player may be required to leave the field of play for two minutes.

There are a few exceptions. If the player indicates he doesn’t need medical attention, if the player removes himself from the field to receive treatment, or if the player is injured on foul that results in a yellow or red card (which Campbell didn’t receive for colliding with Messi).

The rule, implemented last month by MLS, intends to quickly resume play after a player injury, and ensures a player gets adequate treatment quickly.

It also aims to curtail gamesmanship by teams, whose players tried to milk precious time off the clock with an injury stoppage to maintain their lead and hinder opposing teams from making a comeback.

Has the MLS injury rule worked?

Early data shows the MLS off-field treatment rule is working.

MLS reports there have been 1.77 injury stoppages per game in the past three weeks since the rule was implemented compared to 5.25 stoppages.

Further, the new data shows only 0.16 times (roughly 1 in 6 games) did an MLS player need to serve the two-minute wait on the sideline.

Essentially, Messi’s sideline wait was a rare occurrence based on the new MLS data since the rule was installed last month.

Where does Messi, MLS injury rule go from here?

The MLS could argue if Messi wanted to return to play immediately then he should’ve walked off the pitch on his own before being treated by trainers.

It’s just inconceivable for MLS teams to work around the implemented rules when a player’s health comes first.

The first thought when an injury occurs is the injury, not getting off the field in a timely manner so one can re-enter.

Cleaning up gamesmanship is one thing – and appreciated. But having the world’s greatest player openly criticize the unintended consequences of a rule in the middle of a match is another.

Messi’s outspoken – and rare – criticism should inspire MLS to further adjust.