Sadiq completes his move to Real Sociedad on a four-year deal worth a guaranteed €20m, with another potential €6m in add-ons.
The Nigerian forward finally seals a move to Soceidad after being linked to a host of other clubs all summer.
He replaces Alexander Isak who joined Newcastle United last week for a record fee of €70 million
The 25-year-old will bring back aerial threat and strength to Real Soceidad and will be important in competing for European spots.
Sadiq was previously linked to Villarreal this summer but the deal collapsed, providing Real Soceidad a golden opportunity to acquire the signature of the potent striker.