Mr Portillo told BBC TV's Question Time programme that Mr Hague had not yet mastered his handling of TV and came across as "unconvincing" on screen.
The remarks by Mr Portillo, who has developed a broadcasting career since losing his seat, were immediately seen as an unflattering comparison with his own media skills.
Mr Portillo, still seen by some as a future Tory leader, this week began presenting a Channel 4 political magazine; he has also made BBC films. He said Mr Hague had "very great qualities", but his television technique was not one of them. "The difficulty is... those of us who know him think that he's very good and very able, and he's not yet found the way of convincing people through a television screen.
"Television is a different sort of medium. Some people are very well adapted to it, some people have to adapt to it. Certainly it will be necessary for William to develop that extra strand. I'm absolutely confident he can master those techniques over a period of time."