Son, who has been in terrific form for Spurs this season, will miss the home leg next week against the Dutch side through suspension.
"I try to be positive but missing this semi-final makes me so sad, so disappointed," he told Sky Sports.
"I'm a very positive guy, I'm very comfortable with the lads so I'll probably be more nervous watching in the stands than when I play.
"But I trust my team, I trust my players, I trust this stadium so I'm not worried about it.
"Saturday is more important for me, so I'll give everything for my team to get three points and then Champions League is next.
"I want to play every single game. I'm the guy who enjoys my football, with joy and of course I want to play the semi-final.
His absence will be a massive blow for Spurs, who will also be without dependable goalscorer Harry Kane for the remainder of the season after suffering an injury against Manchester City.