Ronaldo was surprisingly left unused in the recent Nations League match against Norway as the legendary forward remained the bench.
The Portuguese Football Federation has called an emergency meeting to resolve the fallout between Cristiano Ronaldo and Portugal manager Jorge Jesus following the final whistle, despite his side picking up a victory on the night.
Reports stated that the 41 year old was unhappy with Jesus' decision not to bring him on as a substitute, having reportedly been promised 30 minutes of playing time.
Portugal face Denmark on Thursday night and ahead of the clash Riemer has spoken on the Al-Nassr forward who he believes is still integral to the nation's success.
"He is a player, I think, people underestimate. They underestimate the importance he has in that squad. I believe that the day he stops with the national team, a big problem will arise in terms of the hierarchy.
"I think he holds it all together with a very, very tight thread, and one should not underestimate the significance of that," the Denmark boss told TV2.
Denmark full-back Joakim Maehl also spoke on Ronaldo, who he has faced four times in his career:
"Of course it's different when he plays. There can be advantages and disadvantages. He is probably a more stationary striker than Goncalo Ramos, who is a little more energetic and harder to cover.
"But there is no doubt that with what he has shown before, you also know his qualities, and on a good day he can also score a hat-trick."
Ronaldo is Portugal's all-time leading scorer and appearance maker with 146 goals in 234 caps for his country. He is currently chasing down 1000 goals and is currently on 979, 21 away from his target.