Spurs are believed to be long-term admirers of the Spanish winger, and even attempted to bring him to the Premier League under former coach Juande Ramos.
Now, Sporting have offered the Londoners the chance to sign the 25-year-old for a reduced fee of around £5m.
The Portuguese giants are currently in a state of financial turmoil, with mounting debts forcing them to sell their star assets.
As a high earner, Capel could be one of the first players out of the door as they look to trim their wage bill in a bid to stay afloat.
Tottenham are thought to be interested, with manager Andre Villas-Boas keen to add reinforcements to help the club compete both domestically and on the European stage next season.
The ex-Sevilla man would provide ideal cover for Aaron Lennon, Gareth Bale and Gylfi Sigurdsson, and could offer an alternative attacking option.
Both Liverpool and Swansea are believed to be interested, but would be unable to offer Capel Champions League football, an opportunity Spurs look likely to be able to present.
Sporting are also looking to sell a number of other players, including another Tottenham target Ricky van Wolfswinkel.
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