Developing and maintaining chemistry is vital to any team's success. No side ever won anything with a team full of players who couldn't work together, and forging constructive working relationships is an absolute must. Clashes between opposing players is inevitable, but on-pitch coexistence is crucial to a team's success, and for 90 minutes, those on the same side can't operate on different wavelengths.
There's nothing to say they need to be best mates behind the scenes though. In fact, some of football's biggest stars have coexisted with teammates they truly despised. Some were able to put it aside for the sake of the team, but others weren't, with their simmering rivalries breeding years of demonstrable bitterness and resentment.
A football club is just like any other workplace. Some employees will become friends, others will forge only polite, professional relationships, and many will inevitably rub each other the wrong way. Add the sport's inflated prima donna egos to the equation, and clashes are inevitable.
Some of these duos were immediately separated when their beef came to light, while others put up with it for years. Either way, there's no denying they hated each other's guts...