Sporting CP head coach Silas refused to deny whether an agreement is in place for Bruno Fernandes to leave the Portuguese club amid links to Manchester United.
Sporting captain Fernandes is reportedly nearing a move to United after officials from the two clubs are said to have been in talks on Saturday (AEDT).
Fernandes was linked to United, Premier League rivals Tottenham and La Liga giants Real Madrid at the start of the season, but a transfer did not materialise as the Portugal international eventually signed a new contract in November.
After scoring twice in Sporting's 3-1 Primeira Liga win over Vitoria Setubal on Sunday, Silas was asked if Fernandes already has an agreement and whether he would be available for the derby against Benfica.
"I can't guarantee any of these things because I don't know," Silas told reporters post-game.
"I'm already thinking about the game with Benfica and I'm thinking about using it [Bruno Fernandes]."
Fernandes has scored eight goals and supplied seven assists in the league this season, while he has netted 15 across all competitions.