The versatile forward has played in a host of positions since joining the club from Nottingham Forest as winger back in 2015 and was deployed in attack in the chastening defeat to Manchester City last week.
However, with Pablo Zabaleta the only right-back available to the 'Hammers' due to Ryan Fredericks' injury and the fact Sam Byram is out on loan and with seven games coming up this month, Pellegrini has warned Antonio that he will be expected to fill in on occasion.
"Against City our most dangerous player was Antonio," Pellegrini explained ahead of Saturday's game against Newcastle. "So on one side I am happy because of the way he is playing and on the other he is not scoring — he must score.
"But he is not a striker. He is a winger who will also play right full back in some games. Unfortunately, we have just one right back and that is Zabaleta. For his age, it is impossible for him to play seven games in December."
The 28-year-old has regularly shown his versatility by filling in at full-back and wing-back when needed, with his powerful physique proving just as useful in defence as attack.