Sir Alex Ferguson has claimed that "foreign players" are the worst culprits when it comes to diving. The Manchester United manager's comments came in response to Sergio Agüero's criticism that there is a bias against overseas footballers from domestic referees in the Premier League when awarding fouls.

Ferguson, who is preparing his side for Tuesday evening's Champions League group game at Cluj, the Romanian title holders, said: "It's not worth going into that subject because down the years there have been plenty of players diving, and you have to say particularly foreign players."

In Saturday's 3-2 home defeat to Tottenham Hotspur at Old Trafford, one of Ferguson's own foreign contingent Nani appeared to be denied a penalty when Jan Vertonghen pulled the Portuguese back in the area. The referee Chris Foy did not award the kick, and while Ferguson does not think the winger is a diver, he did say after the match that the penalty may have been denied due to Nani overplaying the incident.

"There were quite a few [penalty claims]," he said. "I think the one in the first half was a clear penalty kick, but maybe Nani made a meal of it and he didn't need to do that. He was clearly pulled back."

Yesterday Ferguson added: "Nani is not the type to dive, I know that. It was a penalty kick on Saturday. Sometimes you get them, sometimes you don't. The linesman could have helped him but didn't."

Agüero's comments followed Manchester City's 2-1 win at Fulham on Saturday after the Argentinian's fellow countrymen Carlos Tevez and Pablo Zabaleta were each denied penalties when apparently floored in the home area.

Asked if foreign players in the Premier League experience more difficulty than English players winning decisions from match officials, Agüero said: "Yes. Always. But it happens everywhere [in the world]. There is a little bit of privilege with players who come from that country. That is normal. We just play our game, and the referee's job is to know who is tricking him and who is not."

Agüero said he believed that referees were more suspicious of overseas players. "It can happen," he said, "and if it does, it's not good for anyone. Here in England, there are almost as many foreign players as English players and it's not right that some have a privilege that others don't."

While only three penalties of the 17 awarded in the Premier League so far this season have gone to English players this may be because a higher proportion of forwards are of overseas nationalities. The Premier League is thought to be relaxed about Agüero's comments.