Barry Ferguson admits nephew Lewis' two-footed lunge on Tom Rogic was indefensible.
The Aberdeen midfielder was shown a straight red by ref Craig Thomson as Celtic ran out 3-0 winners in a dramatic Scottish Cup semi-final.
The Dons also had Dominic Ball sent off while boss Derek McInnes followed assistant Tony Docherty into the stand after reacting to a sectarian chant from Celtic fans.
Docherty had earlier been sent packing for what was believed to be "unacceptable behaviour".
But Ferguson's rash challenge on Rogic was perhaps the most clear-cut sending off and his Rangers legend uncle has put it down to experience.
He told PLZ Soccer : "That's when you want your experienced guys in the team, to try and calm the situation down.
" Aberdeen were going late into tackles and they were a bit all over the place.
"But I can't defend Lewis. I know he's my nephew but it was a two-footed lunge.
"It comes down to inexperience for me. Aberdeen were missing Graeme Shinnie, who might've told him to calm down and get on the ball.
"I can't defend him, it was a sending-off. I'm sure Lewis will learn from it."
