Cesc Fabregas has played down the contribution of Cristiano Ronaldo at the World Cup and said that Argentina's struggles are not all Lionel Messi's fault.

Writing in a column for BBC Sport, Fabregas, who was left out of Spain's squad for this summer's tournament, said that Ronaldo's four goals in two games, including a hat trick against La Roja, "have come from set-pieces, penalties or mistakes."

Fabregas also praised former Barcelona teammate Messi and bemoaned Argentina's lack of quality as they have drawn with Iceland and lost to Croatia putting them on the brink of an early World Cup exit.

"It was a similar story for Messi against Croatia, but it was not all his fault," Fabregas said. "As I said in my TV analysis after Argentina's defeat, they look like a broken team.

"So it is has been really difficult for him. He does not have the quality in behind him, when he needs someone who can help him build up the play."

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Cristiano Ronaldo has scored four goals at this summer's World Cup so far. Abedin Taherkenareh/EPA

Fabregas -- who played alongside Messi at Barcelona -- says his Ronaldo does not have to work as hard for the team and that explains why he has been able to flourish.

"These days, Cristiano Ronaldo has a very different role for Portugal -- he mainly stays up front and you no longer see him running all over the pitch," he added. "He is one of the big names in Russia who has made a strong start to this World Cup, in terms of goals, with four so far.

"Yes, he is playing well, but if you really look at what he has done, he has scored one penalty, one free kick, one goal from a corner and one with a shot that David De Gea should have saved. You cannot say that he and Portugal have shown great combinations or tiki-taka football to score great goals.

"You have to give him credit, of course, but his goals have come from set-pieces, penalties or mistakes."

Argentina must win their final group game against Nigeria on Tuesday to stand any chance of progressing to the knockout stages, while Portugal need just a point against Iran on Monday to advance.