Sporting manager Ruben Amorim insists Tottenham target Pedro Porro will only be allowed to leave should his release clause be met.
Spurs have watched the former Manchester City youngster and are keen to strengthen at right-back, with neither Emerson Royal nor Matt Doherty proving overly convincing.
Djed Spence, meanwhile, has been handed only 26 minutes of competition action since his summer move from Middlesbrough.
Porro, who played against Spurs in the Champions League, has excelled as an attacking full-back this season, registering nine assists in 20 club appearances.
The 23-year-old was on the books at City between 2019 and 2022 but did not make a senior appearance.
There is believed to be a release clause worth around £39.7m in his contract with the Lisbon giants.
Whether or not Spurs are prepared to match that remains to be seen but Amorim vowed to keep a hold of the player if the clause is not activated.
“With regard to Pedro Porro, we know that there are players in our team who, because of what they have done, are now wanted by other clubs,” he said at a press conference.
“We had this problem in the summer too.
“What I was told is that he can only leave if the clause is triggered. And if the clause is triggered, there is nothing we can do.
“He is playing really well. Like me, he is living one of the best moments of his career and he is only focused on Sporting.
“We are prepared for anything and we know that there are clubs who can pay the clause. But, until that happens, I think Pedro is safe.”