Martin Jol will give Boumesca Tue Na Bangna until January to force his way into Fulham's first team – or send him out on loan.
The Portuguese winger made his debut as a second-half substitute in Saturday's derby defeat at Chelsea.
Mesca, who signed a new long-term deal in April, has leapfrogged Iranian international Ashkan Dejagah in the queue for Fulham's right-wing spot.
And boss Jol has challenged the 20-year-old to fight it out with Bryan Ruiz and Damien Duff for a regular place in the side.
“I told Mesca if he starts scoring goals and giving us assists he could be the number one,” said the Dutch manager.
“I will wait until January [to loan him out] because he's in contention for the first team."