The England under-21 international emerged as a target for both Chelsea and Arsenal towards the end of the summer window. Ex-Gunners centre-back Tony Adams recommended the defender to Arsenal, but reports claimed Chelsea led the race for his signature.
His current deal includes a £4.2m buy-out clause, but the report claims Sporting want to warn off interest from the two Premier League giants by including a massive £40m release clause.
The 19-year-old has a contract at the Portuguese club until 2016, but Sporting want to extend that by two years to the summer of 2018.
As well as the release clause, the report claims Sporting are ready to reward the defender with an improved weekly wage after the teenager broke into the first-team.
A call-up to the England under-21 team earlier this year brought him to the attentions of Arsenal and Chelsea, but he is reportedly happy in Portugal and did not move on deadline day despite reported interest from his native England.