The two mature-aged recruits were promoted under the nominated rookie rule on Tuesday, making them eligible for senior selection.
Cotchin says the former Melbourne forward-turned-defender and the ex-Geelong ruckman are in line for a call up to face Carlton in their season opener on March 28.
"They've both played some really good footy over the pre-season and they've trained really well and almost haven't missed a beat, so I'm sure that will come into its own next week when the side is put out," Cotchin told AFL.com.au on Tuesday.
"Big O has been fantastic; he's going to be there as a support for big Ivan Maric, and Ricky has come into the side and played a defensive role for us.
"I think it's a fresh start for him and he's pretty excited about it, and hopefully both get an opportunity pretty early on in the season."
The nominated rookie rule sees clubs with fewer than 40 primary-listed players able to elevate a rookie before Tuesday's 2pm deadline.
The Tigers only have 38 on their list, meaning they had the option of promoting two players.
Former Essendon midfielder Sam Lonergan was believed to be in the frame but missed out in favour of the reborn half back and the big man.
Petterd, 24, first impressed as a defender in an intra-club match at Punt Road in February, before going on to play four games in the NAB Cup series.
The ex-Demon played 54 games for Melbourne between 2007 and 2012.
Stephenson, 30, played eight games for Geelong last season in his first year on an AFL list.
He made three appearances for the Tigers during the pre-season, as well as playing in the clash with the Indigenous All Stars in Alice Springs last month.
Ricky Petterd is a forward in NAB AFL Fantasy. He averaged 47.25 points in 2012. Register your team at our AFL Fantasy Hub.
Jennifer Phelan is a reporter for AFL Media. Follow her on Twitter @AFL_JenPhelan.
