Stagnant Chelsea in danger of being overtaken by the competition

Arsenal has improved, Manchester City has improved, Manchester United has bought big and Liverpool looks like a brand new side. Chelsea, however, remains more or less unchanged from the side that won the Premier League by eight points, and that inactivity in the transfer window could and should come back to bite the Blues.

Chelsea idling while its closest competition catches up is a curious strategy and one that could well cost Jose Mourinho’s Blues the opportunity to go back-to-back. Refusing to actively reinforce a title winning side should hurt Mourinho either in January – when he is forced to pay above market value – or at the end of the season when the Premier League hardware is handed out.

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Replacing an aged Didier Drogba with misfiring Radamel Falcao may prove to be an improvement for the Blues, but the Colombian is a gamble that is hardly a safe bet given his recent play at Manchester United and with Colombia. First-choice striker Diego Costa missing the Community Shield due to persistent injuries reinforced the misjudgment of not buying a top-level striker that can step in and reliably score goals. Falcao could potentially fill that role, but the 29-year-old has failed to convince since sustaining a knee injury in early 2014.

Costa’s own fitness issues have lingered since his Atletico Madrid days, when he left the 2014 UEFA Champions League final before the 10-minute mark. The Brazilian-born Spaniard had trouble staying healthy at the end of his first season at Stamford Bridge, and he has failed to stay fit during the preseason. Not appearing in the Community Shield warrants a bit of a panic.

Along with a questionable Costa and a misfiring Falcao, Loic Remy has yet to yield returns for the Blues. After scoring 14 goals in 26 appearances for Newcastle United, Remy contributed seven goals in 19 appearances for Chelsea. If Costa’s injuries continue to persist, Remy may be the club's best option for a considerable chunk of the upcoming season.

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While Chelsea has been quiet in the transfer window, cross city and Premier League title rival Arsenal finally added an elite shot-stopper and closest title rival Manchester City added two England internationals. While the Blues napped under a tree, Arsenal and Man City steadily closed the gap on them.

Petr Cech’s odd transfer from Stamford Bridge to the Emirates immediately paid off for Arsenal with a win in the Community Shield. Cech kept a clean sheet against his former club, but more importantly, the experienced Czech international provided the Gunners with security. Seeing the 33-year-old in goal behind the back four immediately resulted in a boost in confidence, rather than the usual fingernail-biting anxiety of a Gunners side that tends to wilt under intense pressure, especially when facing Chelsea. In his first match, Cech broke Mourinho’s spell on Arsene Wenger and Chelsea’s dominance over Arsenal.

Breaking Chelsea’s defensive hold on the Premier League, however, is still a work in progress. Since Mourinho returned to England, the Blues have allowed a total of 59 goals over two seasons, which is 0.78 goals per game and best in the league. The league average over that period of time is 99 goals allowed, or 1.31 goals allowed per game. With Mourinho, Chelsea’s defense concedes roughly 20 fewer goals per season than the average Premier League side.

During the 2014-15 campaign, Arsenal finished with 36 goals allowed, which was only second best to Chelsea’s 32 goals allowed. With Cech, the Gunners should improve on last year’s defensive numbers, while Chelsea’s sales of Felipe Luis and Cech provide the basis for a shift in defensive dominance in the Premier League. Last season, Arsenal allowed under a goal a game for the first time since 2008-09, so the club was already catching up before Cech’s arrival. Back when the Gunners last won the league in 2003-04, the “Invincibles” only allowed 26 goals in 38 league matches.

Chelsea’s title threat is not limited to London, of course. Just as scoring goals is as important as not conceding, the Blues recorded 73 goals last term, but that was with a relatively healthy Costa notching 20 league goals in his first English season. The uncertainty with Costa leads to inconsistency in Chelsea’s attack, which is where Manchester City has a clear edge over Mourinho's men.

Led by Sergio Aguero’s league-leading 26 goals, City’s attack welcomed Raheem Sterling from Liverpool to improve on the club’s league-best 83 goals from a season ago. As one of the best chance creators in the attacking third, Sterling promises to further improve on his seven-goal and seven-assist haul with Liverpool. Based on preseason performances, Sterling sharpens the Manchester City attack in a lethal weapon capable of breaking records.

With City’s habit of winning the Premier League every other year, which notably follows the trend of second-place finishes coming in years where Yaya Toure leaves for the Africa Cup of Nations at midseason, the Citizens make a strong case for finishing the 2015-16 campaign triumphant. Add in Fabian Delph from Aston Villa, who can eventually replace Toure in the midfield, and Manchester City has noticeably gained ground on the champions.

A re-tooled Liverpool and an expensive Manchester United should offer a challenge, but Chelsea, Man City and Arsenal are the three clear frontrunners in the chase for the 2015-16 Premier League title. Man City and Arsenal are catching up, but Chelsea appears content to stand still, which is generally not a great strategy in any race.

Regardless of which team ultimately emerges victorious, Chelsea’s curious stationary transfer strategy over the summer promises a photo finish in May.

Shahan Ahmed is a soccer columnist for Yahoo Sports helping covering the beautiful game globally. Follow Shahan on Twitter: @ShahanLA and @perfectpass