It’s possible, but not likely.

TBH it really depends on the individual situation. Pre-cum or pre-ejaculatory fluid is often released when a guy gets an erection. The function of this fluid is to clean out the inside of the urethra (the tube that carries semen and urine out of the penis) and make it less acidic so that sperm has a better chance of surviving the journey to the vagina. If pre-cum has sperm in it because he has ejaculated recently, the pre-cum can carry the leftover sperm on its way through the urethra and out of the penis. The only way to really prevent this it to make sure that you are using a condom.