Sergio Aguero has been told he is among the best strikers in the world as he prepares to face Barcelona.

The Manchester City striker is aiming to score his 150th goal for the club when Pep Guardiola takes on his old club Barca tomorrow in the Champions League return at the Etihad Stadium.

Aguero scored twice and made one for Ilkay Gundogan on Saturday when City ended their six-match winless run with a 4-0 win at West Bromwich Albion to take his tally to 13 goals this season.

Guardiola has worked with Lionel Messi and Luis Suarez in his time at the Nou Camp and believes Aguero is among the best on the planet.

But he also believes the 28-year-old Argentina international, who has played 221 times for City, could be even better if he shows more belief in himself.

“In the box he is at that level,” said the City manager. “But Aguero has to convince. He's one of the nicest players I ever trained in my career.

“It's a pleasure for me to work with nice people and Sergio is one of the best ones by far.

“But to convince people he has to believe how good he is and how we need him. He has to try that.

“It is not about how many goals he scores because we're happy with the scoring.

“If he doesn't score it is not because I'm not happy with him, his behaviour or body language. “When he is good everything can happen in our team.”

Manchester City's Sergio Aguero (L) celebrates with Ilkay Gundogan after scoring City's first goal (Getty)

Guardiola added: “Never in his career has he been aggressive. I don't want Aguero to run behind the central defenders, I don't want Aguero to jump higher than the other strikers - they're taller than him.

“I'm talking about he has to feel how important he is for us. When he's happy of course all the team is happy.”

Guardiola admitted he thanked his main striker at The Hawthorns after his brace ended a worrying run of results for City.

“I said to him thank you,” said the Spaniard. “We need him. Without him we cannot achieve our target, it is impossible.”

Guardiola also says Willy Caballero is ready to face Messi and Co after Claudio Bravo was preferred at the weekend.

“He's ready - he's played all season and at Old Trafford he played really well and made one or two saves,” said the City chief.

“Like Sergio, he helped me a lot at the beginning when he played and even when he didn't play.

“I have a lot of confidence in him that he'll put in a good performance.

“He has to be ready because he's going to face the best - one of the best strikers in the world is in Barcelona's team. But I have a lot of confidence about his quality.”

Meanwhile, West Brom assistant head coach Dave Kemp has refused to put a time limit on Saido Berahino's return.

The 23-year-old striker, who is out of contract next summer, hasn't played since September 10 and has been put on a weight-loss plan with extra training to lose the pounds.

Berahino has only played five games this season and hasn't scored.

Kemp said: “Saido is closer and he is working hard. When he gets in the team we can start discussing Saido again, but I don't know when that will be.