The Blaugrana forward has had a scan on his recent foot injury and it confirms that the Chile international is facing up to a month on the sidelines.
The 23-year old Chilean was forced to be replaced after just 20 minutes of his country's friendly game against Serbia on Wednesday, and the results from the scan have revealed that he is suffering from a sprained lateral ligament in his right foot.
If the injury keeps the attacker out of play as long as the Barcelona staff fear, then it could potentially keep him out for up to eight games for the club, which means he will miss their crucial Champions League matches against Spartak Moscow and Benfica, while also a top-of-the-table clash with Atletico Madrid.
This will not be his first absence from the Camp Nou outfit, as earlier in the season he suffered from a small tear in his thigh, which kept him out for a short period of time. Sanchez also has a history of returning from international duty with injury problems, which Tito Vilanova will be wary of.
Barcelona received good news in that captain Carles Puyol, who missed several weeks after dislocating his elbow, could be ready to return to action against Zaragoza on Saturday evening. Sergio Busquets, however, is suspended for the weekend's clash.