"Sporting informs that Marat Izmailov was transferred to Porto and that Miguel Lopes was signed with a contract that runs until June 2018 and has a buy-out clause of 20 million euros," Sporting said in a filing to the Portuguese stock market regulator's website.
Russian international Izmailov, 30, joined Sporting in 2007 and has been an influential player in the last few seasons. However, he has been plagued by several injuries of late and sparsely used in the first team.
Lopes, 26, is a versatile defender who can play both as a left and right back and was perhaps the biggest surprise call-up in Portugal's Euro 2012 squad.
Sporting, who sacked coach Franky Vercauteren on Monday and replaced him with Jesualdo Ferreira, provided no further details on the deal or if any transfer fees had been involved.
Porto are second in the league, three points behind leaders Benfica but with a game in hand. Sporting, enduring one of their worst ever seasons, languish in 12th place, one point above the relegation zone.