Rosberg pipped Mercedes team-mate Lewis Hamilton to the drivers’ title in 2016 and quit the sport shortly afterwards.
However, his triumph has received a muted reception by some, who believe he profited from Hamilton’s technical issues.
Saudi Arabian Grand Prix
Hamilton wins drama-filled Saudi Arabian Grand Prix
F1 supremo Ecclestone refused to rank Rosberg alongside the multiple world champions currently on the grid – Sebastian Vettel (four), Hamilton (three), Alonso (two) – instead keeping his praise short.
"Well, let’s just say he is a world champion," Ecclestone said.
"The other names that you mentioned (Hamilton, Vettel, Alonso) have obviously won more than a few times and have achieved more. So I would just call Nico a world champion and nothing else."

Rosberg toasts F1 title success at Mercedes HQ

However, the 86-year-old did concede that Rosberg will be missed in 2017.
"He’s not as popular as Lewis but Nico was a very popular driver," he added. "So his absence is certainly not good for Formula One."

How Rosberg won his 1st title

Saudi Arabian Grand Prix
High drama at Saudi Arabian Grand Prix
Saudi Arabian Grand Prix
Saudi Arabia GP as it happened – Title race to go to wire after more Hamilton-Verstappen drama