The Lions have agreed a €30 million (£26m) transfer for the winger, according to Fabrizio Romano, and the 26-year-old will sign a five-year contract at the Jose Alvalade Stadium.
Romano has even revealed that Zalazar will undergo his medical on Wednesday afternoon, as first reported by A Bola, before sealing his big-money switch.
A versatile attacking midfielder, capable of operating in any position behind the striker, Zalazar is a huge coup from one of Sporting's divisional rivals.
The seven-cap Uruguayan international has scored 23 goals in all competitions and provided assists, predominantly as a central attacking midfielder.
Zalazar will therefore provide quality cover to the likes of Francisco Trincao and Pedro Goncalves next season, while potentially playing in the Champions League.
Sporting can confirm their place in the Champions League qualifiers by drawing or securing all three points against Gil Vicente on Saturday, May 16.