My spouse had blood in his semen after sex?

Hello ! I am writing for my partner because I am worried. We have been a couple for 9 years, we are together every day, so the question of STIs can be ruled out. But today during our protected intercourse (condom) there was blood in his sperm, it's the first time it happened, he didn't seem to have any injury or lesions! We are worried, we looked at a little on the internet and they say that there is nothing serious if it doesn't last. But I still want to have the opinion of a professional before Google. He is just 28 years old. Thank you very much for your help.