The 29-year-old striker completed the full 90 minutes in Valencia's 3-1 defeat to newly promoted Deportivo La Coruna on Saturday, scoring his side's only goal. However, he returned to training on Monday morning while limping, raising concerns over his fitness.
According to Analytica Fantasy, Sadiq could be sidelined for up to two months, potentially ruling him out until late October or early November.
The setback represents a significant blow for Valencia, where manager Carlos Corberan regards the forward as an important squad member who has often produced in difficult situations.
Valencia will now have to rely more heavily on alternatives such as Arnaut Danjuma and Hugo Duro during Sadiq's absence.
For Nigeria, however, the injury is unlikely to cause major disruption ahead of the September qualifiers. Sadiq has not been a regular under head coach Eric Chelle, who has several other attacking options available.
Victor Osimhen remains a mainstay of the Super Eagles setup, with the Galatasaray forward expected to lead the attack. Chelle favours a two-striker formation, making Akor Adams another likely selection despite failing to score in Venezia's opening two matches.
The coach also has Tolu Arokodare, Cyriel Dessers and Rafiu Durosinmi at his disposal, with all three enjoying impressive club form since the beginning of the campaign. The abundance of options could leave Chelle with a difficult selection decision.
