But the dual premiership coach acknowledges it could take time for the key forward to build a connection with his new teammates.
Former West Coast co-captain Allen will debut against the Western Bulldogs at the Gabba on Saturday night after joining as a free agent over the off-season.
"He was jumping out of his skin at training yesterday, that's for sure," Fagan said.
"Like all of our tall forwards, we just want him to provide a really strong contest. Hopefully he can mark a few of those, but if he can't, bring it to ground.
"Given his experience in leadership at the West Coast Eagles, I think he'll be a really handy player in our forward line to help with the organisational side of things.Â
"He's quite vocal, which I really like."
Fagan wasn't too concerned over Allen missing pre-season matches, noting he had completed the workload required.
Allen has already proven a popular member at Brisbane and has been voted into their leadership group, which should hold him in good stead as far as connecting with teammates goes.
"I'm OK with it - he's an experienced player, he's had a lot of campaigns so there'll be a little bit of connection stuff I suppose but that'll take time anyway," Fagan said.
"Oscar's very confident. Socially he's great and mixed in with his teammates really well. It feels like he's been around here for a long time.
"I hope not but it might take a little bit of time. It's sport and building connection and understanding patterns and habits of teammates does take a little bit of time.
"So maybe he will, maybe he won't, but he's done his best over summer to try and make that not an issue."
Fagan was wary of what the Bulldogs, who have impressed in pre-season and have a "stacked" midfield and "quite brilliant" attack, could deliver.
"More than dangerous, they were exceptional last week against Hawthorn. They were up and about," Fagan said.
He added with a laugh: "I actually went down and watched that game live - I was happy when I turned up and I walked away with a few headaches."
If others will focus on Brisbane's bid to emulate the legendary Lions side that completed a three-peat between 2001 and 2003, Fagan won't.
"The start of last year we weren't talking about going back-to-back and this year we won't be talking about trying to win three in a row," he said.
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