Manager Mauricio Pochettino’s high-pressing style means that Spurs expend a lot of energy throughout matches when closing down opposing teams.
And Merson feels that Tottenham’s last Premier League match against Manchester City was the perfect example of his fears.
Spurs managed to beat City 2-1 at the Etihad Stadium, but the former Arsenal midfielder believes that it was only thanks to Pochettino’s foresight that the Lilywhites claimed the three points.
City scored a late goal through Kelechi Iheanacho in the fixture, and they looked the more likely victors in the final stages.
However, Pochettino responded by bringing on Erik Lamela and the Argentine winger’s energy seemed to spark Spurs back into life.
Lamela created Christian Eriksen’s winner and Merson believed that change was the turning point in the contest.
"You worry about Tottenham in the last 15/20 minutes, as they close down so much," Merson said.
"Fair play for Pochettino for putting Lamela on [against Manchester City]. I think if he didn’t put him, they fade out a little bit towards the end of the games.
"But they’ve gone ‘right, I’ll put another forward on’ and I like that."
Despite Merson’s fears, Spurs have a good record this season in the closing stages of matches.
Tottenham have scored 12 times and conceded on eight occasions in the final 15 minutes of contests over the season so far.