Rojas has relinquished his seat with the DragonSpeed LMP2 team with both this weekend's Monza race and next month's Portimao finale remaining on the schedule.
The Mexican shared the squad's #21 Oreca 07 with team mainstay Ben Hanley and Ryan Cullen for the first two rounds of the campaign at Paul Ricard and Spa, with Timothe Buret replacing Cullen for the most recent round, also held at Paul Ricard.
But the best result for the car so far has been eighth in the season opener, and the team's fortunes didn't improve for last month's Le Mans 24 Hours, where Rojas, Buret and Juan Pablo Montoya suffered a litany of mechanical misfortune and retired.
With the #21 car out of action for Monza due to chassis damage, Rojas - who won last year's title with IDEC Sport - has decided to end his association with DragonSpeed.
"In conjunction with my sponsors we have made the decision not to participate in the last two rounds of the season," the Mexican driver said in a statement. "This is because the car wouldn't be ready for the next round.
"After the retirement due to a suspension failure in Le Mans, a structural failure on the chassis was found. They told us that this repair wasn't going to be on time to compete at Monza.
"This adds to the mechanical issues we've faced on the first races of the season. The main goal this year was to defend the title, but it's been impossible because of these situations. It's a difficult situation for us, especially since we won the title last year.
"This is not the first obstacle I've had in my career and this time will definitely allow us to prepare better for 2021, refocus efforts and return to seek to fight for the championship, as well as seek to achieve our ultimate dream which is to win the Le Mans 24 Hours."
#27 Dragonspeed Oreca 07 - Gibson: Henrik Hedman, Ben Hanley, Renger Van Der Zande
Sam Bloxham / Motorsport Images
DragonSpeed will still be entering a car at Monza this weekend, as the team presses its second Oreca chassis into service for Hanley, Henrik Hedman and team newcomer Charles Milesi.
It will be one of 15 LMP2 cars in action at the Italian track, with all but one of those being Orecas as per the previous three ELMS races.
On the driver front, Nyck de Vries will be back for G-Drive Racing alongside Roman Rusinov and Mikkel Jensen for the first time since the Paul Ricard opener.
Algarve Pro Racing is missing Loic Duval for the first time this year due to a date clash with the DTM. Ex-Formula 2 racer Arjun Maini takes the Frenchman's place, sharing Algarve's #24 car with Jon Lancaster and Henning Enqvist.
Tatiana Calderon, Sophia Floersch and Beitske Visser will contest their first ELMS race as a trio for Richard Mille Racing, although this puts Calderon in doubt for the following weekend's Super Formula round at Sugo due to Japan's strict 14-day quarantine requirement.
Calderon was already forced to miss the previous race at Okayama, which followed on a week from Le Mans, and was replaced at Drago Corse by Koudai Tsukakoshi.
#50 Richard Mille Racing Team Oreca 07 - Gibson: Tatiana Calderon, Sophia Floersch, Beitske Visser
JEP / Motorsport Images