The Argentina international, 21, has suffered a frustrating few months in north London since joining from Roma in a club-record £30m move in August, with poor form and injuries restricting him to a peripheral role under former boss Andre Villas-Boas and his successor Sherwood.
His struggles have led some to link him with a temporary move back to Italy, but Sherwood insists the winger will be staying at Spurs and believes he has a huge future at White Hart Lane.
"We know what a talented player Erik is and we also understand how players need time to settle," said Sherwood.
"He's needing that time to acclimatise to a new country. He doesn't speak English and with the tempo of the games, especially over the Christmas period when they come thick and fast, he hasn't been 100 per cent fit.
"He's still feeling fatigued in one of his thighs so we are being very cautious with him. We don't want that to turn into a real injury problem so we're going to take it nice and steady with him.
"I really want to put him on the stage when he's ready to perform rather than let people judge him when he's really half-cooked."
When asked if Lamela had a long-term future at the club, Sherwood said: "Absolutely, he won't be leaving on loan in this transfer window."
Sherwood later confirmed that Benoit Assou-Ekotto would remain on loan with QPR for the rest of the season despite the defender revealing he was keen on returning to White Hart Lane.
Assou-Ekotto admitted he was hoping for another chance to impress following Sherwood's appointment as Andre Villas-Boas' successor, but the new Spurs manager said the left-back "will stay where he is".
But Sherwood may recall young midfielder Tom Carroll, who is also on loan at Loftus Road, to help him recover from his recent fitness problems.
When asked whether Carroll could be recalled this month, Sherwood said: "Possibly, but we are monitoring the situation to see if he can come back to fitness here and how long it might take."