The central defender was first ruled out of action in October following the match with Leeds United at the start of the month, but he was able to make his return since then.
Sierralta did manage to play for Chile during the recent international break after getting back to full fitness, but this led to a further injury taking place.
Claudio Ranieri was not able to use him during the 4-1 victory against Manchester United at the weekend, and that is set to be the case for a little longer.
The Watford Observer have reported that Sierralta is expected to miss the next two weeks' worth of action because of his hamstring injury, which will provide a defensive test for the squad.
The Hornets will travel to face Leicester City at the weekend as they aim to stay above the relegation zone. body check tags ::