Sanchez is the highest paid player in the Premier League after making a blockbuster move to United from Spurs' local rivals Arsenal last week.
The 29-year-old marked his debut by setting up two goals in United's 4-0 beating of minnows Yeovil in the FA Cup fourth round on Friday.
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Despite criticism of his attitude in the latter stages of his spell with Arsenal, Spain midfielder Herrera says Sanchez's grit and desire have rubbed off on his new colleagues and are certain to prove a huge asset.
"What I really like from him is the way he fights when the team loses the ball," Herrera told MUTV. "He's always ready to be the first defender for the team, and that's big for us. Obviously we know his quality on the ball, he's amazing, but his fight, the way he defends, he's the first player to defend. I really like it."
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United manager Jose Mourinho, whose second placed side are 12 points behind leaders Manchester City, clearly agrees with Herrera about Sanchez's catalyst qualities.
It is believed that Mourinho wants Sanchez's positive attitude to work to rub off on the youngsters.
Michael Carrick, who captained United against Yeovil on his first appearance since September, was quick to hail Sanchez's signing as a coup as he labelled the flamboyant playmaker a perfect United star.
"He is not bad is he? Not bad for a little man," said Carrick. "He is going to be a terrific player, he is a proper Manchester United player, and it's great to have him here. He is so exciting and so dynamic. He's always looking to create opportunities."
Meanwhile, Mauricio Pochettino has warned his Tottenham players that he is ready to act in the final days of the January transfer window.
"Of course we have some options," said Pochettino. "We are going in the last few days to see if we can add players that add good quality. If not then it won't happen. But it's about in the next few days to see if we have some possibilities with some players."
Cahill backs Antonio Conte
Chelsea captain Gary Cahill has insisted that he and his fellow players have "no idea" about Antonio Conte's future at the Premier League champions as they prepare to take on Bournemouth on Wednesday.
"It is between the manager and the board. We have no idea about that, we have no idea what's going on between the lines," the England centre-back told reporters. "I have experienced it a lot in my time here, but this has been a successful period. Chelsea is a successful football club and he is a top manager. We can't have any impact."
Third-placed Chelsea are 15 points behind runaway leaders Manchester City and Conte remains under pressure but Cahill insists he still has the backing of all the players.
"Of course we are 100 per cent behind him. There is nothing between the manager and players, whatsoever," he said "If Manchester City hadn't done what they've done, the title would still be there to be won. This season they've been fantastic, but we still aim to fight for second place. We have a big month coming up ... let's hope we come out at the end of that month in a positive way."
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