The Saints suffered a 2-0 loss to Tottenham at St. Mary’s Stadium in the Premier League.
First-half goals from England internationals Harry Kane and Dele Alli proved enough for Spurs to pick up all three points.
Koeman was far from pleased with his team’s performance against the North London outfit and has made his opinion clear on Twitter.
Played well in first 30 min. But defence was bit naive. We failed to show killing mentality, offensive and defensive!— Ronald Koeman (@RonaldKoeman) December 19, 2015
Over the course of the 90 minutes at St. Mary’s Stadium, hosts Southampton had 51% of the possession, took 11 shots of which four were on target, and took four corners.
Visitors Tottenham had 49% of the possession, took 13 shots of which six were on target, and earned seven corners.
Southampton are 12th in the Premier League table at the moment with 21 points from 17 matches.