Guest Post By Greg Lea.

There was not much for Manchester City fans to celebrate at the Etihad Stadium on Saturday evening as they watched their side being comprehensively taken apart by Jurgen Klopp's vigorous visitors from Liverpool. In fact, the only real moment of quality that the hosts could muster was a terrific solo effort from Sergio Aguero making his return from a seven-week lay-off with a hamstring problem that threatened to get City back into the game at the end of the first half.

It was a fantastic goal from the Argentine marksman, who picked up the ball around 35 yards out, dribbled past Lucas Leiva and finished unerringly past Simon Mignolet and into the bottom corner. Although it was ultimately not enough to inspire a comeback Martin Skrtel found the net late on to wrap up a 4-1 Liverpool victory Aguero's piece of magic was a reminder of just how essential he is to Manuel Pellegrini's outfit.

The 27-year-old has been a regular scorer ever since moving to the Premier League in the summer of 2011. His debut against Swansea City was memorable for a second-half brace as Roberto Mancini's men ran out 4-0 winners in the first game of what would ultimately turn out to be a title-winning campaign.

He was prolific before that, too: 23 goals were plundered in 56 appearances for first club Independiente Manchester City Home Shirt 2015 - 2016and 101 in 234 outings for Atletico Madrid during a five-year spell that began in 2006. When the Abu Dhabi United Group parted with around £38m to bring him to England four years ago, they knew that they were signing one of the hottest marksmen on the continent.

The only issue City have encountered with Aguero is his frequent absences from the team due to various fitness problems. He managed only 42 top-flight starts in 2012/13 and 2013/14 combined, and also missed the important Christmas and new year period last term after jarring his knee in the 1-0 win over Everton at the Etihad in early December. Many of the issues have been muscular, which is always a concern for a player as reliant on explosive acceleration as Aguero.

There is little doubt that, when fit, the Argentina international is the best centre-forward in the Premier League; while it is therefore patently a good thing that Man City have him on their books, they know that their domestic and European hopes are hugely dependent on him avoiding another lengthy spell on the treatment table. Wilfried Bony and 19-year-old Kelechi Iheanacho are the only back-up strikers in the squad, and although Raheem Sterling and Kevin De Bruyne can both be used up top, Aguero is by far and away the best option in the City ranks.

Wednesday night's clash with Juventus was typical of Aguero's customary difficulties immediately after returning from injury: the 27-year-old lacked sharpness and struggled to get into the game before his withdrawal in the 69th minute.

Aguero has hit seven goals in nine Premier League appearances this year, though five of those came in a single devastating display against Newcastle United in October. He has also scored once in the Champions League, a vital stoppage-time winner from the spot in the narrow triumph over Borussia Monchengladbach, and another in the Capital One Cup third round defeat of Sunderland.

Those tallies will only increase when he is again operating at full capacity. With the Premier League title race looking as open as it has done in years and Barcelona, Bayern Munich and Real Madrid among their potential opponents in the first knockout round of the Champions League, City need Aguero to stay injury-free from now until the end of the season in May.