Smith Rowe has not been named in the Arsenal squad for his trip to Vicarage Road and the club have confirmed the reason for his absence.
The 21-year-old missed last week’s win over Wolves with what was described as an illness.
And Arsenal have now confirmed that Smith Rowe has tested positive for Covid.
In Smith Rowe’s absence, Gabriel Martinelli retained his place on the left flank against Watford as Mikel Arteta named an unchanged squad.
Arsenal also traveled to Vicarage Road without Takehiro Tomiyasu, who has not recovered from a calf injury.