Both sides have been drawn into a bitter war of words after the end of the summer transfer window, where speculation grew about a move for Sporting midfielder William Carvalho.
Following the closure of the transfer window, Sporting's director, Nuno Saraiva, claimed the East London club never made an offer for the Portuguese midfielder.
The Hammers were certainly less than pleased with Saraiva's claims and will now take legal action against the Primeira Liga side.
On his personal twitter account, David Sullivan Jr. said: "West Ham are commencing legal proceedings against the communications director of sporting Lisbon as a written offer for the player was made.
"To Bruno de Carvalho the president of sporting Lisbon. To say we never made an offer is nonsense and serious libel."
West Ham are commencing legal proceedings against the communications director of sporting Lisbon as a written offer for the player was made
— DAVE SULLIVAN JNR (@DaveSulley) September 3, 2017
To Bruno de Carvalho the president of sporting Lisbon. To say we never made an offer is nonsense and serious libel
— DAVE SULLIVAN JNR (@DaveSulley) September 3, 2017
The Sporting chairman recently gave a statement on the failed transfer saying: "I want to give an information that has come out on both sides that I would like to emphasize.
"I have always defended Sporting to the last, it is often not easy to reconcile the interests of the club and the athletes, but I always strive to do so, but I liked it here that they had a notion that for William there was not a single proposal.
"You could see millions and millions on newspaper covers and televisions, but the fact is that Sporting did not refuse too much or too little because there were no proposals."
Tensions were then cranked up when Saraiva came out with a strongly worded statement, referring to the West Ham co-owner as a lying parasite.