The Belgium international was partly at fault as AS Monaco’s Bernardo Silva broke the deadlock at Wembley in Wednesday night’s 2-1 Champions League defeat.
Thomas Lemar added a second before Vertonghen’s Belgian compatriot Toby Alderweireld halved the deficit to offer the north London side some late hope.
Mauricio Pochettino has started the former Ajax centre-half in all four of Tottenham’s Premier League games so far and Spurs have conceded just two goals so far.
Former Everton and Republic of Ireland international Kilbane delivered his blunt verdict on Vertonghen’s efforts this term following Tottenham’s 2-1 Champions League loss to Monaco.
“Vertonghen is having a bit of a nightmare this season,” Kilbane told Newstalk.
The 29-year-old has been a regular in the Tottenham side since his move to White Hart Lane from Ajax in 2011.
Vertonghen has netted eight times in 162 appearances in all competitions for the Lilywhites since moving to Tottenham.
Tottenham are in fifth place in the Premier League table after collecting eight points from a possible 12.
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