Diego Costa's hamstring injury has been an ongoing issue dating back to his time at Atlético Madrid, but, in recent weeks, it's come to head again following his last trip away with Spain. As well as spending time in hospital for an unspecified illness, Costa returned in no condition to play for Chelsea, having missed the last three matches for the Blues.

While Jose Mourinho was justifiably cheesed-off by the nature of his handling while out on international duty with his adopted country, there have been signs of improvement in the last few days. Rumours of him shaking off the injury and playing a part in the trip north to Old Trafford on Sunday were unfounded, but he did finally make a return to full training today.

Whether he'll be risked so soon - and against lowly Shrewsbury - tomorrow remains to be seen, but he appears to be on track to have some involvement against Queens Park Rangers at the weekend. While it's great news for Chelsea going forward, there may yet be a significant spanner in the works at Stamford Bridge.

According to Neil Ashton of the Daily Mail and NBC Sports, Costa will eventually need surgery to clear up the problem once and for all. Estimates place the recovery time from such a procedure at somewhere around six weeks. Obviously, the club will hope to put it off until the close season and nurse the Brazilian Spaniard through the remainder of the campaign with some combination of duct tape, crazy glue, and prayer.

This report isn't exactly news, as such. Diego Costa is widely-known to have a recurring hamstring issue, and such conditions usually require surgical intervention to fully clear. Thankfully, it's the sort of injury which can be tolerated over a season and dealt with at the earliest convenience.

That's not to say, though, that we're in the clear. First-and-foremost, it will still need to be handled carefully, but it seems likely to lead to other small injuries, which will probably see him missing matches here-and-there. Hopefully they'll be less important than Sunday's match, but we have no guarantees.

In an ideal world, Diego Costa is nursed home to a Premier League winners' medal in his début season, but who can say at this point? Perhaps a major flare-up or a moderate injury involving three weeks or more out will prompt the club to bite the bullet and okay the surgery mid-season. Either way, Costa's long-term future is looking great, but the short-to-medium-term will be a collective squeaky bum time for everyone at Stamford Bridge.