Jose Mourinho and Paul Pogba's relationship at Manchester United has taken another turn for the worse.Pogba questioned Mourinho's tactics earlier on in the week, prompting Mourinho to strip him of the vice-captaincy at the club.Mourinho spoke of his decision after their League Cup exit against Derby on Tuesday."The only truth [to the reports] is that I made the decision for Paul not to be the second captain anymore," he said."But no fallout, no problems at all. The same person that decided Paul is not the second captain anymore is the same person that decided Paul was the second captain - myself."I'm the manager I can make these decisions, no fall out at all, no problems at all. Just a decision I do not have to explain."But footage has emerged from training earlier on Wednesday suggesting that is not the case.The two can be seen having an argument, with Mourinho clearly unhappy with the Frenchman.Mourinho could be heard saying: “Paul, get out” and then telling a colleague to "take Paul home."It was unknown what prompted the argument.But Sky Sports have now provided a caption to the video which could explain why Mourinho was so upset with the 25-year-old.Pogba was rested for the game against Derby and instead watched from the stands alongside the likes of Luke Shaw and Andreas Pereira.And he posted an Instagram video of him, Pereira and Shaw looking on.The video was taken during the game but was posted after the loss against Derby.To be fair, it doesn't look that great on Pogba. Man United fans were unhappy with the video and it seems Mourinho felt the same way.Mourinho can be seen asking John Allen, United's press officer, about the Instagram post and when it was taken.He said: "John, come here please. When did Paul post on Instagram?"Pogba can then be seen trying to defend himself as Mourinho tries to uncover the truth.

So there you have it. The source of the whole argument seems to be the Instagram post Pogba took last night.

You can sympathise with Mourinho. It didn't look very good that Pogba is posting on Instagram laughing and joking when his teammates are playing.

Pogba would be wise to limit his activity on social media from now on.