The Serie A giant's interest comes after Fenerbahce had a bid for former Bournemouth centre-back Kelly knocked back earlier in the week.
Magpies boss Eddie Howe wants Kelly to stay, having brought him in from his old side in the summer transfer window in a free deal.
The 26-year-old has played just 13 games for Newcastle since joining, the 16th most in the Magpies squad.
Kelly was sought after upon becoming a free agent in the summer, having been a regular starter with solid Premier League experience playing across the back four.
And Newcastle won the battle with Howe and the player wanting a reunion.
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However, it hasn't quite worked out this campaign with Lewis Hall replacing him at left-back and now centre-back Sven Botman has returned.
That means any sale would represent pure profit for Newcastle.
Clearly sensing a cheap deal, Jose Mourinho's Fenerbahce made a move for Kelly earlier in the January window but it was rejected.
Yet Juventus may well prove a more tempting option, given the fact they're playing in the Champions League.
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The 36-time Serie A winners are currently 14th in the league phase of the competition, putting them in the play-off places and just two points from automatic progression to the last 16.
Things aren't so straightforward domestically, though, with a massive 13-point gap to league leaders Napoli.
New manager Thiago Motta was on a four-game winless streak to begin the new year, but ended it with an impressive 2-0 win over Milan on Saturday, getting revenge for their Super Cup defeat.
They did so again without Gleison Bremer, who was integral under Motta until an ACL injury ended his season, meaning a defensive reinforcement is desperately needed this window.
Should Kelly make the move, he'd be just the fifth Englishman to play for the Old Lady after David Platt, Samuel Iling, Stephy Mavididi and William John Jordan.
Darren Bent backs Newcastle United in the Premier League title race this season