ORLANDO (Reuters) - Former Real Madrid forward Kaka has called on the team's fans to show more respect to Cristiano Ronaldo, who was booed during a La Liga match against Celta Vigo earlier this month.

Ronaldo became Real's all-time top scorer this season, and has scored 41 goals in all competitions in the current campaign, but the Portugal forward continues to endure a fractious relationship with the club's supporters.

"Cristiano is a great player and I'm not just talking about his quality, but what he has contributed to Real Madrid...," Brazil international Kaka, who now plays for Orlando City in the MLS, told Spanish radio station Cadena Cope on Wednesday. "I'd like to see supporters show more respect to Cristiano for what he has done for this club. Hearing people boo Cristiano is not right after everything he has done for this club."

Ronaldo, who responded to the booing in the Celta Vigo match by scoring four goals in the second half in a thumping 7-1 win, is top scorer in La Liga this season with 28 goals.

He is two ahead of Barcelona forward Luis Suarez as he bids to become the league's No. 1 marksman for a third straight year.

The Portuguese overtook Raul as the Real's all-time top scorer last October, grabbing 324 goals in 310 matches, compared to the 741 games the Spaniard needed to score 323.

The 31-year-old also set a record with 11 goals in the Champions League group stage this term, but has been criticised for failing to score in the biggest games against teams like Barcelona, Atletico Madrid and Paris Saint-Germain.

He was also criticised by fans and team mates alike for his derisory comments after the derby defeat by Atletico on Feb 27, when he said: "If everyone was at my level we would be top of the league".

Former World Player of the Year Kaka joined Madrid for 65 million euros (S$99.5 million) in 2009 - the same year as Ronaldo arrived for a then-world record 80 million euros - but left in 2013 after failing to live up to expectations.

The 33-year-old Brazilian said the Bernabeu club is an unforgiving place even for the best players in the world. "When you go out to play for Real Madrid you know what it's like, it's not just like that with Cristiano, it has been like that with (Zinedine) Zidane, Raul, (Iker) Casillas... it has always been like that," added Kaka. "The only thing I would like is to see a little more appreciation of what Cristiano has done there, which is a lot."