Following his return to full training duty on Monday, Brahim had been included in his side's 22-man roster ahead of Madrid's 3-1 away win over Celta de Vigo in their La Liga opener on August 17, reports Efe news.
"After the tests carried out today on our player Brahim Diaz by the Real Madrid Medical Services, he has been diagnosed with a muscular injury to the anterior part of his right thigh," the Madrid club said in a statement.
"His recovery will continue to be assessed."
Ahead of the ongoing campaign, Brahim was announced on July 14 to be the first to be sidelined from the Madrid squad with a hamstring injury in his left thigh.
He sustained the injury during his team's pre-season camp in Montreal, Canada, which kept him out of action for 34 days.
Brahim moved to Madrid in January 2019 on a transfer from England's Manchester City, making a total of 11 appearances with the Spanish club last term; nine in La Liga and two in Copa del Rey.
The Malaga born winger, who has Moroccan roots, joined Madrid's "sickroom" which also includes summer acquisitions Ferland Mendy, Eden Hazar and Rodrygo, as well as Marco Asensio, who still continue with their recovery programmes.
Mendy, however, has been permitted to partially train with his teammates.
Costa Rican striker Mariano Diaz also worked out in the gym.
The remainder of the squad completed two training sessions on Tuesday under French coach Zinedine Zidane who called Diego Altube, Fran Garcia and Takefusa Kubo from the Madrid B-Team to join the practice.
Being the first leader of the La Liga standings, Madrid is set to host Real Valladolid in a matchday 2 encounter scheduled for Saturday.
( With inputs from IANS )