This is a randomized (study medication assigned to participants by chance), double-blind (neither the researchers nor the participants know what treatment the participant is receiving), placebo-controlled, multicenter (when more than one hospital or medical school team work on a medical research study) study to evaluate the effect of JNJ-63623872 in combination with oseltamivir in participants with influenza A infection. The study consists of 3 Phases: Screening visit (1 Day), participants who meet all eligibility criteria will be randomized in a 2:1 ratio to receive study drug in double-blind treatment Phase (7 Days) and follow up Phase (21 Days). The duration of participation in the study for each participant is approximately 28 Days. Primarily Pharmacokinetic parameters of JNJ-63623872 will be measured. Participants' safety will be monitored throughout the study.