"French club Lille turned down the chance to sign Vincent Janssen because their manager Marcelo Bielsa had doubts over the Tottenham striker’s technique."
https://www.standard.co.uk/sport/football/lille-turned-down-move-for-tottenham-flop-vincent-janssen-due-to-doubts-over-technique-a3629766.html
But he can't score when you take away the two pens handed to him on a plate by empathetic team mates. Levy and Pochettino almost succeeding in making a profit on a PL dud.
Lamely hasn't really lived up the £30m fee, which was a huge fee in 2013. He did later improve in quite a few home games, but as you say the injury has been another blow.