Lining up on the grid in fourth place for his home race much was expected of the reigning MotoGP Champion.
However, his 2015 title defense instead went from bad to worse.
Chasing Jorge Lorenzo for the lead, Marquez had to take evasive action after almost touching the back wheel of the Yamaha.
That resulted in his going off the track at Turn 10 and crashing out of the race.
He explained: "I tried to give 100 percent at my home race but I made a mistake trying to push too much, as I wanted to do well – at all costs – and these things can happen.
"I was going well, trying to conserve my tyres behind Jorge, but I made a mistake and as a result I ran wide. When I was in the gravel I saw the wall was very close, so I leaned over a little but I couldn't stop the bike.
"I was able to ride back to the garage, but I soon realised the gear lever was damaged and I was unable to shift gears."
With his third retirement in seven races, Marquez has managed just 69 points and trails Championship leader Valentino Rossi by 69.
Marquez added: "I want to thank the fans who came out; the best thing about the day was hearing the cheers from them during the three laps I rode."