Arsenal captain Laurent Koscielny's decision to boycott the club's pre-season tour over a contractual dispute is the latest blow in an unsettling summer for the Gunners.

Facing a third consecutive season outside the Champions League, Arsenal are attempting to play catch up with their rivals at the top end of the Premier League on a far more restricted transfer budget.

AFP Sports looks at the key troubles facing Unai Emery's men ahead of the new season.

Koscielny's standoff with the club reportedly comes after Arsenal rejected his request to have the final year of his contract terminated to secure a longer deal and a return to France.

However, even if the 33-year-old remains, Arsenal were already looking to strengthen a defence that conceded 51 goals in finishing fifth in the Premier League last season and four to Chelsea in a Europa League final loss that cost the Gunners a return to the Champions League.

A bid for Celtic left-back Kieran Tierney has been rebuffed with Arsenal reluctant to meet the Scottish champions £25 million ($31 million) valuation.

A deal for highly rated St. Etienne centre-back William Saliba for £27 million is reportedly near completion, but only on the agreement the 18-year-old returns to the Ligue 1 side on loan next season.

Rob Holding and Hector Bellerin will miss the start of the campaign as they work their way back to fitness following knee ligament injuries, while Shkodran Mustafi has been deemed surplus to requirements following his calamitous end to last season.

At the heart of Arsenal's struggles is the loss of Champions League revenue after 19 consecutive seasons in the competition between 1998/99 and 2016/17.

A booming wage bill due to the signings of Pierre-Emerick Aubameyang, Alexandre Lacazette and Henrikh Mkhitaryan, plus the bumper contract renewal for Mesut Ozil in January last year has also taken its toll.

That has left reportedly just £45 million net spend available for transfers this summer and a £40 million bid for Crystal Palace's Wilfried Zaha was laughed off by the Eagles, who want at least double that for the Ivorian.

Arsenal's budget could be supplemented by sales, but maximising value from departures is another area where they have fallen behind their top six competitors.

Aaron Ramsey was allowed to leave on a free transfer to join Juventus after running down his contract.

In amassing attack-minded talents in Aubameyang, Lacazette, Ozil and Mkhitaryan the Gunners are over-subscribed at the top end of the pitch and lack cover elsewhere.

Aubameyang and Lacazette have at least delivered on their club-record transfer fees with goals, but Emery's preference to play with just one striker has meant often one of the two has to start on the bench.

Ozil and Mkhitaryan have been peripheral figures at best under Emery, but are happy to sit on lucrative contracts that other clubs will not match.

Fenerbahce dismissed suggestions they could be a destination for Ozil this week saying "under the current economic conditions, such a step is not possible for both parties."

Most galling for many Arsenal fans is that their decline has coincided with Tottenham's rise to become the dominant force in north London.

Spurs reached the Champions League final for the first time last season, have moved into a new 62,000 capacity stadium and can look forward to Champions League football for the fourth consecutive season.

Moreover, Tottenham have closed the financial chasm that existed between the clubs. Just three years ago, Arsenal's revenue was £140 million a season more than Spurs.

Based on the financial results for the 2017/18 season that advantage had been whittled down to £10 million and Spurs' Champions League progress will likely see them pass Arsenal's revenue for the 2018/19 campaign.

That new-found financial muscle is beginning to be flexed by Tottenham as they smashed their club record transfer fee to buy Tanguy Ndombele from Lyon earlier this month.