Madrid are due to resume their season against Eibar on Sunday, having not played since losing 2-1 at Real Betis on March 8, with the coronavirus-enforced suspension coming into force soon after that.
With matches to come thick and fast over the coming month, as teams prepare for weekend and midweek fixtures, squad depth could be more crucial than ever.
Nacho, who has already missed a chunk of the season through injury, was likely to enjoy an increase in playing time in the final weeks of the campaign as Zinedine Zidane juggles his defenders to keep them fresh.
But he is now a doubt for at least their first game back, with Madrid yet to confirm how serious the muscular injury is.
A statement read: "After the tests carried out on our player Nacho Fernandez by the Real Madrid medical services, he has been diagnosed with a muscle injury in the right anterior rectum [thigh]."
Madrid are two points behind pacesetters Barcelona prior to LaLiga recommencing.