"I always talk about the opposition team because if I mention one player in particular then there are stories that Barca are interested in him when that's not the case," said Rijkaard.
"But if I have to mention one, then Ferguson is the key player. He has already played a long time for Rangers and he represents the spirit and the mentality of the team.
"Besides that, he is also technically very good. He can shoot from distance and reads the game very well. Often it is necessary for a club to have one player who draws all the attention and keeps things going. Ferguson is like that."
Rijkaard added: "For me, Scottish football has always been something quite special.
"Recently, there have been good results for the national team and also for Rangers in the Champions League. I know the clubs are using a lot of Scottish talent and that is very positive. Scotland is a football nation and it's always a pleasure to play here."