Sunderland defender Younes Kaboul was partly at fault for the first goal that his side conceded.
Kaboul was largely excellent against Leicester City earlier today, but one lapse in concentration proved costly for the centre-back.
The French defender was caught out by Jamie Vardy’s pace for Leicester’s first, which meant that Sunderland had to chase the game.
The Black Cats ended up losing 2-0, and Souness feels that Kaboul was largely at fault for the defeat.
“The thing that separates teams which are competing for trophies and are at the bottom is that their players learn,” Souness said.
“They make a mistake once and learn from it. Kaboul, you look at him and think he’s got decent technique, powerful, he can run but he makes mistakes like that and that’s cost them the game.”
Kaboul had a ropey spell in Sunderland’s defence over the start of the season, but he has improved under Sam Allardyce.
The powerful defender has formed a decent partnership with Lamine Kone, but the pair could just not keep Jamie Vardy at bay.
Vardy’s pace came to the fore in the second half, as Leicester secured a crucial victory for their title chances.
The defeat was painful for Sunderland, however, as Allardyce’s men are now four points adrift of safety with just six games remaining.