Hart hit the headlines for two mistakes against Bayern Munich last week, but Ruddy believes that the Manchester City keeper should retain his place in England's starting lineup for their upcoming World Cup qualifier with Montenegro on Friday.
The 26-year-old told Sky Sports News: "Joe's the England number one. Rightly so. The way that he's performed over the last few years, he's deserved it and he's never let England down.
"I've been in situations before when people are questioning you. It's never nice. Without being too patronising, I felt sorry for him.
"He doesn't warrant that sort of attention. He's a top-drawer goalkeeper, one of the best in the world without a shadow of a doubt."
Ruddy and Celtic's Fraser Forster are challenging Hart for a place in the starting lineup for the match at Wembley.