The 28-year-old was axed from Aliou Cisse’s 23-man squad despite a fine season with his Premier League side – where he got eight goals and two assists in 22 English topflight games.
Niasse had returned to the Teranga Lions’ fold after a two-year absence in the international friendly against Uzbekistan which ended in a 1-1 draw at the Stade Mohammed V.
With his omission, AS Monaco’s Keita Balde, Stoke City’s Mame Diouf, Amiens’ Moussa Konate, Bursaspor’s Moussa Sow, Torino’s Mbaye Niang, Liverpool’s Sadio Mane plus Rennes duo of Diafra Sakho and Ismaila Sarr will lead the eight-man frontline.
Despite the aching snub, the former Lokomotiv Moscow forward took courage to send a goodwill message his Russia-bound countrymen.
"Here we go! We are Senegal, all the best," Niasse wrote on Instagram.
Senegal must get past Poland, Colombia and Japan in Group H for a chance to reach the Round of 16. They face the Polish team in their first game on June 19, before following up with a date with the Asians on June 24.
Their last group game billed for the Cosmos Arena, Samara holds on June 28. Cisse’s men are hoping to surpass the quarter-final hurdle – their best ever finish at the global football fiesta achieved in Korea & Japan 2002.