The South Korean superstar is coming to the end of his current contract in north London but is currently in sporadic form as Spurs struggle.
Defensive injury issues have hampered Ange Postecloglou's team in the Premier League.
They have, though, reached the League Cup semi-finals where they will face Liverpool, and are well-placed in the Europa League too.
Son has 13 goal contributions 21 appearances across all competitions but wasn't anywhere near his usual self against Liverpool and Nottingham Forest.
That form has led former Premier League striker Tony Cascarino to query if the 32-year-old will get the new deal he wants.
Read more on Tottenham
Tamworth spark controversy with ticket prices for Tottenham FA Cup clash
Jamie O'Hara names Premier League boss who should immediately replace Ange Postecoglou
And he believes there is a chance the next five months could be his last in north London, insisting sometimes difficult decision need to be made.
He told talkSPORT: "I don't think Son will stay at Spurs. No, I don't. I think it's one of them that you've got to make a big call on as well.
"He's been brilliant for them over the years, but it's time to move on in football sometimes."
Tottenham do have the option to extend the South Korean's deal but talks are ongoing over a renewal.
Most read in Football
Bellingham and brother Jobe delight young fan by 'agreeing' to join Championship club
Tamworth spark controversy with ticket prices for Tottenham FA Cup clash
'Horrendous' - Sir Jim Ratcliffe sucking Man United's soul with latest cost-cutting move
Stoke City name ex-Premier League defender as caretaker manager after Pelach sacked
However, Cascarino is insistent it would take a big resurgence in form for Spurs to pull the trigger on a new deal.
He added: "He will survive, or they would definitely keep him, if he had a second part of the season that was superb.
"If he has that season where it hasn't really worked to now, and then he goes and gets 15 or 12 goals in the second part of the season, plays well, then Tottenham will probably use that option.
"But as it is today, I think it's more likely that he could go."
Son, now the club's all-time top assister in Premier League history, is not the only top-flight star in this predicament.
Kevin De Bruyne is in the same bout but Cascarino believes Man City's decision about retaining the Belgian playmaker relies on how fit he is.
He added: "It's another big call for Manchester City, because if it's a fit Kevin De Bruyne, then you've still got one hell of a talent. He still won't lose his ability to pass the ball.
"But they look a team a little bit like Manchester United. They're running out of legs on the pitch in many different positions."
Nottingham Forest striker Chris Wood is also out of contract in the summer - and has been in fine form.
Cascarino, though, believes he should easily be able to claim a new contract from his current employers.
He added: "I think Chris Wood, Forest will try and give him another year, because he doesn't rely on pace.
"You're talking about a player that never has to think about, 'Oh, he's lost half a yard'. It doesn't matter if Chris Wood loses half a yard.
Read More on talkSPORT
Man United fans fed up with Hojlund after spotting angry reaction during Wolves defeat
Floyd Mayweather splashes out $20m on lavish Christmas gift for three-year-old grandson
"If you've got Anthony Elanga one side and Callum Hudson-Odoi the other, and Morgan Gibbs-White joining him, and Elliot Anderson joining him as well, you don't really need to worry about that.
"He could do another year, no problem. So I don't see that as an issue."
Simon Jordan criticises Spurs boss Ange Postecoglou for his attitude towards the media