The man is suffering from a chest wound and has several broken ribs, EFE news agency quoted the hospital’s emergency department as saying.
Two other runners were also hospitalized after Tuesday’s early-morning stampede - one a local man of 36, and the other a 23-year-old Japanese citizen. Both are suffering from more superficial injuries.
In all, 26 people received first aid from the Red Cross service after Tuesday’s run.
Aside from the bull running, by mid-afternoon on Tuesday Red Cross workers had attended to 44 people this week in the streets of Pamplona, 36 of whom required hospital treatment. The volunteer association DYA Navarra had dealt with 35 people in difficulties, mostly caused by alcoholic intoxication.
Four people were injured in the first bull run on Monday.
One 52-year-old man was injured after a bull gored him in the thigh, while three others received fractures, Spain's La Vanguardia newspaper reported.
Fifteen people have been killed in the bull runs since records started in 1911.
The most recent death took place four years ago when a bull gored a 27-year-old Spaniard in the neck, heart and lungs.