The UFC is instituting stricter coronavirus testing guidelines ahead of its return to Las Vegas this weekend.

The promotion sent a memo, which was obtained by ESPN, to the fighters competing on the Las Vegas card scheduled for Saturday. The event will be held at the UFC Apex arena, which is located at UFC headquarters.

Per sources, these are more detailed and stricter than the guidelines in place prior to the three shows in Jacksonville, Florida, earlier this month.

MMAJunkie.com first reported the details of the memo.

All athletes and fighters will now be required to take two COVID-19 antigen oropharyngeal swab tests prior to competing: once upon checking into the athlete hotel and another time following Friday's official weigh-ins.

Test 1: The UFC is requiring every person who is tested upon checking in to self-isolate within the hotel until they receive their results.

"This means you should not leave the Athlete Hotel or have physical contact with anyone other than the members of your camp until you have received your test result," the memo reads.

The memo goes on to state that if the test result is negative, "you may continue with your fight week activities. If your result is positive, you should remain in your hotel room and await further instructions from UFC's medical team."

Test 2: Following the second swab test after Friday's weigh-in, those tested will be required, per the memo, to self-isolate within the athlete hotel and remain inside overnight until their scheduled departure to the UFC Apex on Saturday afternoon.

"During this time, no athletes or cornermen will be permitted to leave the Athlete Hotel without express prior approval from the Nevada State Athletic Commission," the memo reads. "You also should not have physical contact with anyone other than the members of your camp."

If the test result is negative, the athlete and their corner may proceed to the event. If not, they will have to await further instructions from the UFC medical team.

The memo also states that the UFC's Performance Institute will not be open for use during this time. It does not mention daily temperature checks or antibodies testing, which occurred in Jacksonville.

In addition, the UFC is asking the fighters and cornermen to sign a HIPAA authorization form to allow the specified testing lab to share the tests results with the promotion.

UFC 249, the promotion's first event since the COVID-19 lockdown, was held on May 9 in Jacksonville. The athletes who competed on that card ended up taking two swab tests, but that wasn't the original plan. The reason for the second test, which occurred following the weigh-ins, was because the initial test results were not scheduled to arrive in time for the event. The fighters who competed on the subsequent two events on May 13 and 16 took only one swab test before competing.

Ronaldo "Jacare" Souza, who was scheduled to compete on the May 9 event, and two of his cornerman were the only ones who tested positive, per the UFC. Souza was removed from the card -- as well as the hotel -- once his positive result was revealed.