Tottenham’s calm approach to business during the January transfer window was a sign of their stability, but they still lack players who can change a game from the bench.

Only two of Spurs’ goals in the League this season have been scored by substitutes. One was crucial — Heung-min Son’s equaliser in the 2-2 draw at Manchester City last month — while the other, also scored by the South Korean, put Spurs 3-1 up at Southampton in December, where they eventually won 4-1.

Son’s attributes make him a very effective replacement, but he is a rarity — and if another attacking player is unavailable, the 24-year-old will often be needed from the start.

Both Arsenal and Manchester City have seven goals each from substitutes, while Manchester United have five. Though Chelsea and Liverpool have only three goals each from the bench, it is still more than Tottenham.

Perhaps Spurs might regret not pushing a little harder last month to sign one of the players they admire. There were enquiries about Everton’s Ross Barkley and they may look again in the summer, as they surely will at Crystal Palace winger Wilfried Zaha.

Spurs manager Mauricio Pochettino was open to doing a deal for Southampton attacker Jay Rodriguez, but his club did not wish to let him leave mid-season.

Tottenham have certainly invested in their squad. Though their net spend is substantially lower than those of their closest rivals, they have still been active in the market.

Yet, while they are adept at improving their first XI — Dele Alli, Toby Alderweireld and Victor Wanyama have all done so since joining the club in the last two years — they are less successful when seeking to provide back-up.

Moussa Sissoko and Vincent Janssen cost nearly £50million combined, but Pochettino does not have complete faith in either of them.

Georges-Kevin Nkoudou, a £9.5million signing from Marseille, has made virtually no impact and is currently sidelined with a knee injury. Harry Winks is a fine midfield prospect but not yet a game changer.

In most matches, what Tottenham have is enough. When the majority of their key men are fit, they can see off nearly all Premier League opponents. Yet, in games when they must find another way, such as last night’s physical battle at Sunderland, Pochettino lacks choices.

The Argentine is frustrated at the slow start Spurs have made to their last two League matches, against Manchester City and Sunderland. The relative weakness of the bench makes it harder for him to effect significant change.

“It’s clear something is wrong from the very beginning in the last few games,” he said. “At Sunderland, we competed for only the 45 minutes of the second half.”

Though they came from 2-0 down to draw 2-2 at Manchester City, Spurs were lucky. Against Sunderland, who started the night bottom of the table, they struggled to create clear chances.

At Liverpool last night, Chelsea summoned Cesc Fabregas and Pedro, two World Cup winners, from the bench. The home side brought on Sadio Mane with 15 minutes remaining and left Daniel Sturridge kicking his heels.

Arsenal could not avoid a 2-1 defeat by Watford but Alex Oxlade-Chamberlain, who replaced the injured Aaron Ramsey, and Theo Walcott were given the chance to do so. How Spurs could have done with even one of those six players.