Maguire was slammed for his individual performance for England against Germany on Monday night, with the Reds defender conceding the penalty that led to Ilkay Gundogan's goal.
Speaking on Sky Sports on Wednesday, Kelly said: "I can sympathise. He has taken a lot of flak of late and and a lot of the brunt for the good form of United, and since their upturn he's not been involved. So it's almost gotten worse and after coming into the England set-up, he was hoping to have a really good international break and the couple of mistakes have just highlighted him again.
"It's difficult but when you think over the course of football, I always picture the David Beckham incident, when he got sent off at the World Cup. That was like nothing I've ever seen before. Players have received huge amounts of criticism and it's about how they bounce back and how their character is. That's the world we live in now.
"It's relentless so he [Maguire] has to have a really tough skin to be able to get through all that but players are capable of dealing with it. A player like Maguire, he's got to look to come through the other side."