This season, Ziyech has contributed 17 goals and 14 assists in 36 matches for Erik ten Hag's side, who are in the hunt for their first European title since 1995 and their first Dutch Eredivisie honour since the 2013-14 campaign.
Despite his starring displays, Pienaar who played for the Amsterdam outfit between 2001 and 2006, described Ziyech as a joy to watch but he is not getting the attention he deserves as one of the best-performing players this season.
"Ziyech is one of the players that has been playing really well all season, he's the type of player that when you watch him in action, he makes you happy," Pienaar was quoted by KickOff .
"He's a complete footballer, but underrated, you know if you're not European, you are always underrated."
The Atlas Lions begin the quest for their first Afcon title since 1976 with a fixture Namibia on June 23.