Jose Mourinho says the arrival of Baba Rahman will increase competition in Chelsea's defence following a humbling 3-0 defeat at Manchester City.
The Portuguese was critical of his defenders' first-half performance in the clash at the Etihad Stadium, even resorting to substituting John Terry for the first time in the Premier League ahead of the second period.
Asked whether it was his the worst half of football he had seen from his side, Mourinho commented: "Defensively? I don't know. But we were defensively poor in the first half, that's clear."
News of Rahman's arrival from Augsburg for an undisclosed fee broke shortly after full-time and Mourinho welcomed a timely boost to his defensive ranks.
"It's important because he is a left-back and he can compete with [Cesar] Azpilicueta," said the Chelsea manager. "At the same time, by being a left-back, Azpilicueta can compete with [Branislav] Ivanovic for the right-back position.
"This player replaces Filipe Luis in the balance of the squad. He is a player that we need for that balance."
Despite berating his side's first-half showing, Mourinho - who suggested City should have seen Fernandinho and Yaya Toure sent off in separate incidents - believes Chelsea's display in the second 45 minutes merited some reward.
"In the first half the best team was winning, in the second half the best team was Chelsea," he added. "They were the best team in the first half - they controlled the game, they created chances.
"We were very comfortable with the ball, but defensively we were quite fragile.
"In the second half I think everything changed. We brought our defensive line to the midfield line, we pressed them up and had control of the game.
"We created chances, we had lots of space in midfield to play and they couldn't cope with that.
"I'm nobody to analyse the opposite manager's work, but I don't think anybody will misunderstand me if I say he did very well because he felt the result in danger [and made the right substitutions].
"We were punished by our mistakes in the second and third goal and we couldn't capitalise on the good second half we did."