Mauricio Pochettino delivered a “wake-up call” to Vincent Janssen in his office after the striker’s underwhelming start to life at Tottenham Hotspur.

Janssen has scored once in the Premier League since his move from AZ Alkmaar last summer and has fallen out of favour in recent months but the possibility of Harry Kane missing the next six weeks with an ankle ligament injury has increased the pressure on a player who has struggled to justify his £17m fee.

Although Tottenham celebrated the 22-year-old’s first goal from open play in the FA Cup quarter-final win over Millwall, he has rarely looked mobile enough in the Premier League and Son Heung-min is expected to deputise for Kane for Sunday’s visit of Southampton. Janssen has not started since 8 January and, although Pochettino has stood by him in public, the manager has been tougher in private.

“He needed a wake-up to be reminded that the possibility of playing could arrive,” Pochettino said. “He is very young. He came from Holland. I’m happy with him and all the players but I understand they are not happy with some situations.

“The wake-up call is more private inside here than in public. From the beginning of the season some players need a wake-up call in private. In my office.”

Four of Janssen’s five goals for Tottenham have come from penalties but Pochettino hopes the player can push on from his cool finish against Millwall last Sunday . “He is motivated, confident,” he said. “He is feeling a little bit of relief after his first goal from open play and that is important. I am happy in the way that he trained this week too.”

Tottenham found goals hard to come by when they were without Kane earlier in the season. The Premier League’s joint-highest scorer limped off after rolling an ankle against Millwall and Pochettino has said the injury was similar to the one sustained in September, when Kane was out for seven weeks.

However, the fact the swelling has gone down is encouraging and Tottenham anticipate a recovery time of up to six weeks, which means Kane could return for the FA Cup semi-final against Chelsea on 22 April.

Kane has not allowed the setback to weigh him down and has told Pochettino he is targeting a swift recovery time. “We need to assess day by day,” Pochettino said. “He’s positive. He’s talking about after the international break, three or four weeks. That’s good but we need to be careful with his injury. We have full trust in our doctors and physios.

“We hope that as soon as possible he can be available again. If not four weeks, it’s five weeks or whatever. But he’s positive and if you’re positive it can affect in a big way the injuries.

“He wants to play tomorrow. I had to tell him we don’t play tomorrow, the game is on Sunday. He’s like a horse.”