Southampton's management team were left disappointed after their defeat to Sheffield United in the Capital One Cup last night.
The South Coast club had gone into the game with the Blades as heavy favourites, but they failed to find their top level in the match and crashed to a 1-0 defeat.
Sheffield United had not been on the best form in League One this season, but Bob Harris' goal just after the hour was enough to provide them with a memorable victory.
It keeps the Blades good record in cup competition over recent times up, but Southampton fans, players and managers were all left feeling crestfallen after the loss.
Koeman's side had looked to be in with a great chance of making the semi-finals of the competition, but their season is unravelling of late.
Without a win in league five matches, Southampton have dropped out of the top-four and this cup defeat means that confidence at St. Mary's has been shattered.
It led to Koeman and Kluitenberg apologising to fans of the club on social media site Twitter, after they travelled in their numbers to Bramall Lane.
Disappointed result tonight! Feel sorry for our fans! We keep going!— Ronald Koeman (@RonaldKoeman) December 16, 2014
Thanks for the fans who where in Sheffield. Sorry for the result. I am also very disappointed. Wish you all a safe journey at home.— Jan Kluitenberg (@jankluit) December 16, 2014
Southampton's attention now turns to their weekend clash with Everton and they will know that they need to collect the three points in the match to get their season back on track after a very disappointing run of results.