The pair have already exchanged text messages but will meet face-to-face on Monday when the first-team begin training to face Arsenal in the Carabao Cup semi-final.
Cahill believes that Barkley has the necessary talent to make it at Chelsea and says that the fee paid for his services represents a bargain.
"Phenomenal," Cahill said in reaction to Barkley's move to the Blues. "I think it is a great signing. It is a bargain. Looking at this market, in this day and age, it is a snip for a player like him. I’ve played with him and trained with him and I know what the boy is capable of, so does everyone else.
"He’s capable of whatever he wants, if you look at him, he reminds me of Ruben [Loftus-Cheek] in terms of his attributes. Has he got a good left foot? A good right foot? Is he strong? Is he quick? And can he finish? Is he good on the ball? He ticks all the boxes.
"All he needs is a platform just to go and express himself. This club will give him that, like they gave me and gave to other players. It is a big step and it is a good signing. For the money, it has to be a bargain.
"He’s come at a great age. He’s a fantastic age. I say [to him] come here and be confident, but not arrogant. Be confident, but listen and learn from the top players at this football club. Work hard at your game and then you will progress. He knows what he’s got to do.
"Listen, you’re not talking about a young player here. We’re talking about a player that has got over 20 England caps and a player that has played so many games in the Premier League. Even at such a young age, he won’t be needing too much advice from me.
"I’m sure he has that hunger. I text him before he came to see where he is and what not. I think he trained yesterday so I will bump into him on Monday when I get back [to training]."
The draw means Chelsea now face eight games in 28 days and, while Cahill has experienced the intensity of winter schedules for over a decade, he still believes a break would be beneficial to England-based footballers.
"Yes, we knew before, you draw the game and you have a replay," Cahill said. "It is not ideal for most teams and that’s probably it, it is probably a punishment for not performing the way we should have done.
"I am not saying for the [lack of] effort because the effort was there. In the second half we tried and tried but the first half felt flat. The amount of games is incredible.
"We have a ridiculous amount of games at the minute and I said after the game the other day that it is mad. We don’t have a winter break and instead of having two weeks on a beach, we have even more games, so it is what it is.
"The manager changed the team today so we should have been fresh [versus Norwich]. Are we feeling it compared to teams in the other leagues? The Champions League teams that are going to be starting the second stage of their season? Possibly, who knows. It is intense.
"This December and January is intense. Listen, I’ve played in this league for ages so I know all about it. For the lads who are coming in it is different, having another game on top of all that now is not easy for us.
"I think it is an interesting debate and I can say that because I have been involved in it for 10 years or whatever, and I can say that because it has never bothered me before. I only looked at it this year when you look at players coming from overseas and they tell you the kind of schedule that they’ve had over Christmas.
"Last season and the season before in the Champions League all the English teams struggled to get into the later rounds. Why do you think that might be? It is not an excuse, it is just a fact.
"If you come to the latter part of the season, you’ve had two halves of the season, then it isn’t rocket science, you are going to feel fresher. 100 per cent. We don’t, so the boys that have come over are finding that a little bit intense now.
"I can say that, I am from here and I have never had a winter break so it is normal for me."