It is hard not to feel sorry for Vincent Janssen. Short of rhythm, form and confidence, the striker must wonder how many more opportunities he will have to shine for Tottenham.

Janssen cost £17million from Dutch side AZ Alkmaar last summer — a pretty expensive gamble. He has scored three times — all from the penalty spot — in 23 appearances for Spurs. His start against Aston Villa yesterday was his first since the 3-2 win over West Ham on November 19.

Try as they might, Tottenham cannot find a centre-forward to provide reliable back-up for Harry Kane — and Janssen does not look to be the answer. If they are to continue to challenge for major trophies, they need to find a solution.

When Kane missed 10 games with an ankle injury earlier in the season, Spurs won four of them, scoring 13 goals — five of which were against League One club Gillingham in the EFL Cup. Kane was rested for the win over Villa but before that, he featured in 12 straight matches — eight wins, one draw, two defeats, 29 goals scored.

More alarmingly, where Kane takes nearly three shots per game in the Premier League, Janssen’s average is 1.3. Only seven of his 20 shots have been on target. It is not as though Janssen is missing chances. The problem is that he is rarely in a position to miss them.

Janssen looked a little grumpy when he was brought off after an hour against Villa but he had no reason to complain. The Dutchman had only one shot in the match and caused few problems for the Championship side’s back four. As soon as Dele Alli replaced Janssen, Spurs were a different team.

“He needs to work hard and not be frustrated,” said Spurs manager Mauricio Pochettino. “It was tough but not only for him.

“Look at the game we played against Chelsea [which Spurs won 2-0 last week]. Both forwards, Harry Kane and Diego Costa, struggled in the first half. In the second half against Villa, Vincent Janssen started to find more space but we decided to put Alli on.”

So the next time Tottenham enter the market for a forward, they have to get it right. Strikers are the most coveted players in the game and competition to sign them is fierce. In recent years, Tottenham have had more bad ‘uns than good ‘uns.

In 2014-15, his first full season, Kane’s displays forced Emmanuel Adebayor and Roberto Soldado out of the side and the more established forwards never looked like regaining their spots.

In 2015-16, Kane was Spurs’ only orthodox centre-forward. Heung-min Son is happier attacking from wide, while Clinton Njie — now on loan at Marseille — was as ineffective through the middle as he was on the flank. Attempts to sign Saido Berahino from West Brom and Moussa Dembele, then at Fulham but now with Celtic, ended in failure.

Berahino has been close to Spurs many times before and may be so again. Even though the forward has played only five times this season, he is out of contract at its conclusion — meaning he will be available at a reduced fee. Dembele’s case, though, is the really interesting one.

Tottenham thought they had a deal for the Frenchman, then 19, last January for about £4m, plus add-ons. Dembele’s contract expired last summer and he had no plans to sign another, hence the lower price. His wages were manageable and he has rich potential – pace, strength, finishing power and unpredictability. Yet when Fulham decided they wanted Dembele loaned back for the remainder of 2015-16, Tottenham lost enthusiasm. It was also suggested that Fulham asked for 20 per cent of any future sale. Tottenham took a long, hard look and decided to pass.

In the meantime, Dembele signed for Celtic last summer and has scored 19 goals this season. Yes, the Scottish Premiership is inferior to the Premier League. But Dembele’s haul includes a hat-trick in an Old Firm derby against Rangers and two in the 3-3 draw with Manchester City in the Champions League. He will spend at least this season in Glasgow but if Celtic decide to sell in the summer, they would ask for at least £30million.

How Spurs must wish they had taken Dembele. As a young, improving player, he would have been the perfect understudy to Kane, while also ensuring the England striker stayed on his toes.

Such is Kane’s professionalism that he is unlikely to drop his standards in training but he knows that he is an automatic starter regardless of form. It is hardly an ideal situation.

Ten minutes after Janssen had departed, Pochettino sent on winger Georges-Kevin Nkoudou for centre-back Toby Alderweireld. Before that, though, Spurs lined up with a three-man defence for the third match in a row — suggesting this, rather than a 4-2-3-1, is now the preferred formation for the remainder of the campaign.

Nkoudou has work to do to gain the trust of Pochettino but he produced an impressive cameo here. His cross created the opening goal for Ben Davies — his first for the club — before his lofted pass started the move that led to the second for Son. If only he could play up front when Kane is not available.

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