In a wild transfer market, Kyle Walker's fee makes sense for Manchester City

Kyle Walker's expensive switch from Tottenham Hotspur to Manchester City has prompted plenty of bewilderment and criticism. Sources told ESPN FC that the clubs had agreed a fee of £45 million with a further £ 5m in add-ons while the agency that represents the 27-year-old claimed the deal was a record for a defender and an Englishman -- thus beating the £ 50m Paris Saint-Germain paid for David Luiz and the £49m City spent on Raheem Sterling.

Either way, Walker hasn't come cheaply and the size of the fee has led to a backlash. Former England and Spurs striker Gary Lineker was among them tweeting: "Don't get me wrong, I like Kyle Walker. He has many assets, and is a good addition for Man City. Not his fault of course, but £ 50m is mental."

But a move for Walker makes plenty of sense. Here are five reasons why City are justified in paying such a sizeable price for the England international.

Full-back position has been overlooked for years

City's squad is relatively well-stocked in most positions with one glaring exception: full-back. Before the arrival of Walker, Pep Guardiola had just one senior option -- Aleksandar Kolarov -- who spent much of last season playing at centre-back.

Pablo Zabaleta, Bacary Sagna and Gael Clichy -- all in their 30s -- were allowed to leave for free after years of under-investment in the position. City haven't spent any money on a full-back since a relatively modest £7m fee paid to Arsenal for Clichy six years ago.

It was a surprise that in Guardiola's first summer at the club he didn't bring in any new full-backs with his options already in decline. Zabaleta was a fantastic player in his nine years at the Etihad, but a series of injury setbacks and testing seasons led to a dip in the Argentinian's form, and Clichy and Sagna were not the quality Guardiola was used to at previous clubs Barcelona and Bayern Munich, where Dani Alves and Philipp Lahm were so important.

If City also add Monaco's Benjamin Mendy, as they are expected to, they are adding two full-backs who will make a huge difference to the quality of their starting XI.

Best available

A look at the list at the world's best right-backs shows that Walker was probably the best that City could sign this summer. Lahm has retired, Real Madrid would not consider selling Dani Carvajal and Atletico Madrid's Juanfran, Stephan Lichtsteiner of Juventus and Borussia Dortmund's Lukasz Piszczek are all in their 30s and on the decline.

City wanted Alves -- more of that later -- and showed interest in Arsenal's Hector Bellerin before he signed a six-and-a-half year contract at the Emirates.

Walker is certainly in the top 10 right-backs in the world and was the best viable option for Guardiola.

Full-backs are key to Guardiola's game plan

Last season, the Catalan coach expressed his frustration that his full-backs weren't able to cope with his high demands. "We don't have full-backs to go up and down, up and down, because all of them are 33, 34-years-old," he said after a goalless draw with Manchester United in April.

Walker is used to a heavy workload after being an important member of Mauricio Pochettino's side, where he was expected to supplement attacks as well as defend. He contributed five assists from his 33 Premier League appearances -- more than Zabaleta, Kolarov, Sagna and Clichy combined.

And he was the quickest player in last season's Spurs squad, another big asset for Guardiola, who already has a squad packed full of pace.

Premier League premium

Players moving between Premier League clubs cost more than those coming from abroad and City will not be the only team to pay heavily for someone who has proven he can perform in England. Across the city, United have paid £75m for striker Romelu Lukaku, who has not played a single minute of Champions League football, and was discarded by Chelsea early in his career.

Elsewhere, Swansea reportedly want £50m for Gylfi Sigurdsson, Southampton will only sell Virgil van Dijk for £60m and Bournemouth have spent £20m on Nathan Ake. It's a crazy market, but English clubs -- buoyed by extra cash from another improved TV deal -- are ready to pay extra for ready-made signings, so City's deal for Walker is not that extraordinary in comparison.

Alves mess

The way Alves snubbed City left the club vulnerable and forced them to secure a quick deal with Tottenham. The Brazilian was all set to join up with former boss Guardiola until PSG sensationally hijacked the deal.

City's desperation for full-backs is clear and they could not afford to let their chase for Walker drag on until late in the transfer window with Spurs' chairman Daniel Levy notorious for getting his way in his transfer dealings.

Without Alves, City lost their bargaining power and decided to agree a deal before losing out on a potential target, and it gives them some extra time to identify a second right-back to bring in this summer.