Man City's Sergio Aguero warns Barcelona he'll be firing on all cylinders for their Champions League clash

Aguero made a goalscoring return from injury against Blackburn. Photo: PA

Fit-again Man City star Sergio Aguero has warned Barcelona he will soon be back up to top speed.

Aguero needed just 50 seconds to get back on the scoresheet as he returned from injury in City's 5-0 thrashing of Championship side Blackburn at the Etihad Stadium on Wednesday.

After eight games out, the Argentinian was introduced as a 72nd-minute substitute in the FA Cup third-round replay and less than a minute later he was celebrating his 20th goal of the season.

His return slightly ahead of schedule adds further strength to a City side already in fearsome form and firing in four competitions.

City are unbeaten in 16 games - 14 of them victories - and have already scored a remarkable 99 goals in all competitions.

The domestic events may be the immediate priority but it is only a month before the Champions League campaign resumes with a glamour tie against Barcelona and Aguero is relishing the prospect.

The 25-year-old told City TV: "I'm very happy. I couldn't wait to come back. It's been a great recovery.

"I trained with the team on Monday for the first time and here I played some minutes to start bringing myself back on form and to find my pace to play in such a fast football game.

"Maybe in a week I'll be on top form. Obviously the more you play the better you feel.

"Against Barca I will be ready.

"But we still have time and first we need to think about the next Premier League games which are very important, and then we'll think about Barca.

"I hope I can play a little bit longer on Saturday and take it step by step."

Aguero scores less than one minute into his return from injury

Aguero sat on the bench as the City attack was again led by Alvaro Negredo and Edin Dzeko, who have both thrived in his absence.

But a City side showing eight changes - the two strikers and Fernandinho being the only survivors from the weekend win at Newcastle - initially found the going tough against Blackburn, as they had at Ewood Park earlier in the month.

City were subdued and the match was evenly contested until Negredo headed the opener on the stroke of half-time.

The Spaniard then clipped in his second, his 21st of the season, early in the second half to put City in command.

Rovers rallied and twice went close through Josh King but Dzeko ended all doubt with the first of his double after 67 minutes. The Bosnian wrapped up the scoring after Aguero had made his dramatic entrance.

James Milner almost scored City's 100th of the season with a late free-kick that flew wide, but the century seems likely to be reached as Cardiff visit Eastlands in the Premier League on Saturday.

City, a point off the top, have won all 10 of their home league games to date, scoring 38 goals in the process.

Aguero said: "I think we are doing very well. We have improved a lot since the beginning of the season.

"We must keep working like that. We are all playing very well.

"We are building a great team and we need to continue trying to score more goals."

City will play another Championship side in Watford in the fourth round on January 25, by when they are likely to have confirmed their place in the Capital One Cup final.

They travel to West Ham for the second leg of their semi-final next week leading 6-0 after the first meeting.

Manager Manuel Pellegrini has made clear he does not intend to slacken off in any competition and Aguero insists Watford - beaten by City in the third round last year - will not be taken lightly.

He said: "Every team is difficult. Now we must play against Watford so we must prepare for that game well and try to go through to the next round, which is the most important thing."

Milner was not surprised Aguero was quickly back into his stride.

He said: "That is him all over. He is a quality player and it is great to have him back. It didn't take him long.

"Hopefully that run of form keeps up for the next few games."