Chelsea boss Maurizio Sarri has acknowledged that he was unhappy with his side's performance against Videoton in the Europa League.
A second-half effort from Alvaro Morata secured a 1-0 victory for the Blues, who remain three points clear at the top of Group L.
However, the Londoners were expected to make lighter work of their Hungarian opponents, and Sarri has admitted that he had been left unimpressed by the display.
The Italian told BT Sport: "I don't think we played well, we have done a good offensive phase and had a lot of ball opportunities but we conceded too much.
"We have to play every three days, it is very difficult and so we have to have a great mentality. There is a risk to arrive at a match without the mental power and energy. I am very happy with my squad.
"It is a very important in this period of the season to get results, it is not easy but I will have to change a lot players for Southampton and it is not easy to prepare the next match tomorrow - a lot of players will be tired."
Chelsea's win at Stamford Bridge has extended their undefeated streak in all competitions to 10 matches.
