Update dropdown list based on previous selections

Hi,

I would be very grateful if someone can provide help on this one..

I am stuck on being able to update a drop down list of values, so that it will only show the remaining unselected values from previous selections.

The scenario is as follows...

Column A contains 'x' amount of players, columns B, C, D, E etc contain the drop down lists of selectable teams for a number of weeks within the sports season. Every player can select a team once, which means the next used column must remove the team from the previous week. In the situation that the competition is still going by the time all team's have been selected, then the process starts again.

I attach an example of what I am trying to achieve.

Regards

darthlawb