BARCELONA (REUTERS) - Real Madrid's opponents should brace for a re-energised Cristiano Ronaldo, after the Portuguese international forward said he had been following a special training regime to hit peak shape in the final stretch of the campaign.

The usually prolific Ronaldo has had his quietest campaign in front of goal in LaLiga since 2010 but made an emphatic return to form on Wednesday by scoring both goals as Real earned a crucial 2-1 first-leg win over Bayern Munich in Wednesday's Champions League quarter-final.

Ronaldo has arrived at the end of the last few campaigns in a bedraggled state, and last season sustained a thigh injury which forced him out of crucial games, and stunted his performances.

He gave lacklustre displays in the 2014 and 2016 Champions League finals against Atletico Madrid, even though he scored an extra-time penalty in the former match, and struck the decisive spot-kick, with the latter game ending in a penalty shoot-out.

Over exertion in the 2013-14 campaign may also have lead to his disappointing display at the World Cup Finals in Brazil, where Portugal were eliminated at the group stage, while he injured his knee in the Euro 2016 final against France.

Ronaldo had scored twice in his previous eight Champions League games, and had failed to find the net in any competition for a month, but on Wednesday he netted twice either side of half-time to end the German champions' run of 16 straight home wins in the competition.

Ronaldo, Real's all-time top scorer and a four-time Ballon d'Or winner, also became the first player to score 100 goals in Uefa competitions.

"I made radical changes to my training to get to this stage of the season in the best state possible," Ronaldo told reporters.

"In the last few years I got to the end of the season at the limit and with small injuries, but I have worked hard with our fitness coach to be in the right shape for the final two months. The team is playing well, and so is Cristiano."

Ronaldo's comparatively low goal tally this season had seen his detractors claim the 32-year-old was on the decline, although his team-mate Marcelo criticised those who had questioned his displays this term.

"I don't know if it's envy, but Cristiano's numbers speak for themselves," said the Brazilian international defender.

"It's difficult to contemplate what he has done for football, and he is still playing at a very high level."

Ronaldo, meanwhile, gave a bemused reaction when asked by a reporter if he had proved his detractors wrong.

"I don't know who doubted me," Ronaldo said. "The people who love Cristiano never had any doubts."