Tim Tebow's gonna need a miracle to make it in his NFL comeback ... so says Charles Barkley, who thinks it'll be "impossible" for the former quarterback to switch to tight end.

Chuck gave his honest opinion about the 33-year-old signing with the Jacksonville Jaguars with "Waddle and Silvy" on ESPN Chicago this week ... saying he likes Tebow as a person, but has serious doubts about his chances at making a real impact on the field.

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"I think it's going to be very difficult for him to just pick up football, another position," Barkley said.

"Tim's such a good dude, but you know, a lot of people don't like Tim because his religion. He wears it on his sleeve. I don't care about that. I like the kid, but I don't think he can just come pick up another position."