The Serie A giants landed Ndombele on loan from Spurs in the summer, paying the north London club a fee of €1m.
A purchase option set at €30m was also included in the agreement, but it was considered to be unlikely that Napoli would want to trigger it and pay such a sum for the Frenchman.
However, according to Italian outlet Calciomercato.com, Napoli are now entertaining thoughts of considering triggering the clause.
They have been pleased with his recent performances and if he continues to shine then they may be willing to sign him permanently.
Ndombele is out of favour at Tottenham and the club are keen to shift him off the books for good.
The 25-year-old has made eight appearances in Serie A for Napoli so far this season and featured in their 3-2 win over Bologna on Sunday.
Napoli sit on top of the Serie A standings following the win, two points clear of second placed Atalanta.
