Christensen suffered a left thigh muscle strain during the match against Sevilla on 20 September and has missed roughly six weeks of action, including key fixtures for Barcelona and the Danish national team.
Christensen was keen to join the Danish squad but due to the rehabilitation process was forced to stay in the Catalan capital.
"Andreas loves the Danish national team. I can tell you that the man on the other end of the line last night (Sunday, ed.) was practically in tears, because he is so frustrated and upset about this," said Riemer, continuing:
"But the situation is that Andreas is currently undergoing a rehabilitation process. And joining the national team camp—where we wouldn't be able to manage that for him (as he does with his physiotherapist and trainer at his club)—isn't feasible."
"He has assessed that he isn't ready for that. Consequently, he has withdrawn, concluding that, given his current state, his body isn't prepared to play two international matches. It truly breaks his heart," he adds.
According to Brian Riemer, Barcelona didn't put pressure on Christensen to withdraw from the two upcoming Nations League fixtures. In fact, the decision rested solely with Christensen himself.
"There is a big difference between pressuring a club and pressuring an individual. You have to respect the person. Ultimately, it is his decision," the national team coach concludes.
On Saturday evening, Denmark will face Portugal away from home. Three days later, they will host Norway at Parken Stadium in Copenhagen..