The England international has had an indifferent season for the Toffees with Koeman questioning whether he will ever become a top class player.
Everton fans have also been critical of the 23-year-old.
Ross Barkley's horror tackle on Jordan Henderson during Merseyside derby
Tue, December 20, 2016Should Ross Barkley have been sent off for his horror tackle on Jordan Henderson during the Merseyside derby
Should Ross Barkley have been sent off for this horror tackle on Jordan Henderson?
But Gerrard, who played with Barkley at international level, believes he is being harshly treated.
The former Liverpool star told BT Sport: "I'm a big fan of Ross, but what I will say is he has been inconsistent and the Everton fans use him as an easy target.
"I think he's been harshly criticised by Ronald Koeman in the media and that won't be helping him.
"He's their bright spark for the future because he's young and people talk about building a team around him.
"He's 23 and still has 10 quality years ahead of him."