Striker Holmes scored his first goal of the season as Barnet picked up their first point in a 1-1 draw with Bristol Rovers on Tuesday night.
The 25-year-old is now leading Barnet's attack after McLeod, who scored 22 goals last season, opted to leave Underhill over the summer to join Portsmouth.
"He has got that in his locker, Ricky, and he has been like that most of pre-season and in the games we had," said Robson.
"He tired a bit as the match went on and we needed to freshen things up a bit so we brought him off. But he is a top player and in this division he can excel."