Portugal captain Cristiano Ronaldo criticized Luxembourg's stadium as a "potato field" and said he was not in good physical shape in recent games after Sunday's 2-0 win to qualify for the 2020 European Championship.

Ronaldo scored the 99th goal for Portugal towards the end of the game after scoring a hat-trick in a 6-0 win over Lithuania three days ago, but he was far from his level in Sunday's match against Luxembourg at the José Bartel Stadium, whose ground was damaged by the rain.

"It's hard to play on stadiums like this, it was like a potato field and I don't know how teams like us can play on these pitches," the Juventus striker told reporters. "It was not good, but we did our job.

The 35-year-old joined the Portugal squad in February despite speculation about his physical condition and behavior after his angry reaction when he was substituted during a 1-0 win over Milan last week.

After that match, Juventus coach Maurizio Sarri said Ronaldo had a knee problem for some time.

"In the last three weeks I was playing and I was tied, but there is no controversy about what it raised. I tried to help Juventus, and no player likes to be replaced, but I understood because I was not in good shape."

Ronaldo said he was not in 100 percent good form in Portugal.

"I sacrificed myself for the team. We could not have qualified for the (European Championship 2020). Fortunately, I haven't had many injuries in my career but this could happen."

"It is the pain that keeps me from playing 100%, but I always try to get involved. You caused controversy at a time when there was no need to do so. I will be back soon."

Portugal finished second in Group B with 17 points, three ahead of Serbia, who drew 2-2 with Ukraine.

Ronaldo could only become the second player to reach 100 international goals. "The 100th goal will come," he said. "The records are made to break it and I will break it."

Luxembourg suffered a 100 per cent defeat at home to the 8054-seat Yossi Barthel.It was built in Luxembourg in 1928. It was named after the legendary runner Yossi Barthel, who won the gold medal in the 1,500 meters at the 1952 Olympic Games in the Finnish capital Helsinki.

Luxembourg are set to play their next matches at their new stadium, which began construction in 2017, and will be ready this year, and will be named 'National Stadium', according to the Luxembourg Football Federation, and can accommodate more than 9400 spectators and cost about 65 million euros.