Just watching the game back and have noticed there appears to be something (about the size of a credit card) stitched in to the shirts at the back under the collar.

Is this to track players during the game do you think ?

If this is the case then there is nowhere to hide.

The players do wear some kind of GPRS trackers so probably

yea its gps, not every player wears them, but they will be doing soon, it can be tracked live, but they normaly download it all onto the laptop the day after the game and make spreadsheets of players stats and give them out to them on training days

Don't they wear them alongside heart rate monitors so they can get a brief idea on who is working their hardest and who is slacking?

It seems strange that some players were one but not all of them.

yea they wear the heart moniters aswell and the gps have accelerometers built into them, but they dont have enough for every player at the minute as its an expensive system. its not so much to see whos slacking, its to help the players see what then can improve on in there game.