As reported by Goal.com on Monday, the defender came in to replace Pablo Zabaleta for Wednesday's late 1-0 win over Wigan but his boss could not hide his disappointment in the 24-year-old's performance.
"I think that he needs to work a lot," Mancini remarked to reporters of Richards. "I didn't like it [the performance]. "I am happy because he comes back to play but I thought that he was in better form.
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The Italian conceded, howeer, that it was crucial to allow Zabaleta to refresh his batteries after a prolonged spell in the side while Richards was unavailable, explaining: "Pablo has played a lot of games, it was important to give him a break."
With only three days having passed since their tense FA Cup semi-final win over Chelsea, Mancini felt that his players suffered from fatigue against the Latics.
"We had to work really hard because Wigan played very well," he observed. "Every game that we play against them is difficult because they play football and they play to win every game.
"I think we didn't play very well because we were so tired. Only in the last 20-25 minutes we improved and played better.
"There's only three days and for this reason we play with the four, five new players because we spent a lot of energy against Chelsea and it was difficult."