Leverkusen sporting director Rudi Voller confirmed on Wednesday that the South Korea international had travelled to London to undergo a medical with Spurs, though he insisted no agreement over a fee had yet been reached.
But Calhanoglu cannot see why his team-mate would leave Leverkusen - who finished fourth in the Bundesliga last season and defeated Lazio 3-1 on aggregate to reach the Champions League group stage on Wednesday - for White Hart Lane, and believes Son's decision may be influenced by family pressures.
"I think he is badly advised," Calhanoglu told reporters when asked about Son. "I have written to him, called him, but he has not answered his phone. I am very sad, the whole team is a bit disappointed.
"When you're 23 years old, of course you have respect for your father. But you have to sometimes make your own decisions. We were there for him always - that's why we are sad. Everyone has tried to reach him."
Tottenham's move for Son throws fresh doubt on the north Londoners' long pursuit of West Brom striker Saido Berahino after the Baggies rejected a second bid - believed to be in the region of £22 million - for the England Under-21 international on Tuesday.