Diego Costa
Costa's injury will be a big blow to ChelseaReuters

Chelsea are worried about the fitness of Diego Costa after the striker reportedly sustained a hamstring injury during training.

Although the severity of the injury is yet to be confirmed, as the 25-year-old is still undergoing some tests at Cobham, there are fears that the Spain striker could be sidelined for up to six weeks, according to the Guardian. 

If Costa, who arrived from Atletico Madrid for a £32 million fee this summer, is sidelined for a lengthy period, it will be a big blow for the Blues as the Brazil-born striker has been in good form, scoring two goals in two games in the Premier League season.

Chelsea boss Jose Mourinho will probably be forced to look for a new striker before the close of the summer transfer window as the Blues' other attackers are not that reliable.

While Didier Drogba, who re-joined Chelsea on a free transfer this summer, will not be as clinical as before due to his age, Fernando Torres has failed to find consistency at Stamford Bridge.

The West London outfit would probably be looking to make a move for Roma's Mattia Destro, Monaco's Radamel Falcao or Paris Saint-Germain's Edinson Cavani.

Earlier there were reports of the Blues offering Torres in a player-plus cash deal for Destro. Although now there are speculations about the 30-year-old Spaniard joining AC Milan, Chelsea may be willing to re-offer the Spaniard to Roma in an attempt to secure the £20 million-rated striker's signature.

Falcao, on the other hand, is reportedly available on a season-long loan for £20 million. The Colombian is believed to be interested in sealing a short-term move to London, but his £20 million price-tag plus his wages could prove to be a stumbling block.

Finally, Cavani could be the answer for Chelsea if they are prepared to pay PSG asking price – believed to be in the region of £50 million.

The Blues have been interested in the Uruguayan since the time he was at Napoli. But, Cavani opted to join the French side for a reported €64.5 million (£51.3).

Now the 27-year-old is reportedly looking to make a move out of PSG after getting tired of playing second fiddle to Swedish striker Zlatan Ibrahimovic.

Chelsea, however, may face some competition for Cavani's signature, as Arsenal are also believed to be interested in the Uruguayan.