Manchester City have lodged an official complaint to UEFA after alleged racial abuse to some of their players during Thursday’s Europa League game at Porto.

Team-mate Yaya Toure told Sky Sports News: “I heard something.

“That’s why we like the Premier League, it never happens there. Maybe other countries don’t expect black players.”

Tournament organisers Uefa said they were still waiting for reports from their match delegates, which are usually received one or two days after each match, before deciding whether to take any action.

After the game it was revealed that Balotelli had told a club official he had been subject to racial abuse from the stands.

In the post-match press conference, Mancini insisted that the chanting had not disturbed him.

“I didn’t hear the noise, because I was concentrating on the game,” he said.

“I think Mario Balotelli and Yaya Toure are too strong [to be affected].”

Mancini reserved special praise for Balotelli, calling his performance “calm”.

“I think Mario did very well, he played very well,” he said. “He was calm and it is important he continues like this.”

Meanwhile Manchester United’s Antonio Valencia faces up to a month out of action after suffering a hamstring strain in their Europa League win against Ajax.

Second-half goals from Ashley Young and Javier Hernandez sealed a 2-0 victory in the Netherlands.

Substitute Valencia injured himself while combining to produce United’s second goal in Amsterdam.

“It looks like a bad one,” said manager Sir Alex Ferguson of the Ecuadorian’s injury.

With United leading 1-0 courtesy of Young’s low shot just before the hour mark, Valencia had been on the field for just over 10 minutes when he supplied the ball to Wayne Rooney, who fed Hernandez for the goal.

While the visitors celebrated a valuable second away strike, Valencia was quickly replaced by Danny Welbeck.

The midfielder will now be out until mid-March and will miss the return leg with Ajax at Old Trafford on 23 February, as well as Premier League games against Norwich, Tottenham, West Brom and Wolves.

After the game, Ferguson described his side’s performance at times as “very ordinary”.

“We didn’t play well at all in the first half,” he added. “I’m delighted with the scoreline, but I think it was very ordinary.

“We didn’t really hit any great heights, but we did improve in the second half and we probably deserved to win it.”