Southampton suffered a major blow during their 3-0 loss against Premier League champions Manchester City after midfielder Morgan Schneiderlin picked up an injury and had to be replaced at the interval.
According to the Daily Mail, this was the turning point in the game as the Cityzens took the lead at the start of the second half through a deflected Yaya Toure goal. It is believed that had Schneiderlin been there, the Ivorian would not have been in that position to score that opening goal.
The French midfielder has been a key player for Southampton this season and is one of the main reasons for their incredible run, which has seen them occupy second place in the league from the start of the season until they were knocked back to third by the defending champions on Sunday.
The Saints travel to the Emirates Stadium to face Arsenal on Wednesday and then host Manchester United in a Monday night fixture at St Mary's and the manger will hope that his key player will recover in time for these fixtures, which will test their ability to go head-to-head with the Premier League big guns.
Even the manager admitted that the loss of Schneiderlin could have played a part in their loss to City, as he is an important player for them. A player for whom, they do not have a readymade replacement, as Maya Yoshida, who came on in the French international's place struggled to keep pace and contain Manuel Pellegrini's men.
"Maybe, it is always a little bit influence in the game because he's an important player for us. We don't have 24 players what they have to change in the second half for example, we know that," Koeman said, as quoted on Southampton's official site.