Crowley and Kelly joined the Bombers in the past two days as part of a special AFL-approved recruiting allowance in the wake of the Court of Arbitration for Sport's ruling last week which suspended 12 Essendon players for the entire 2016 season as a result of the club's controversial 2012 supplements program.
Essendon can sign as many as 10 top-up players before March 15 and upgrade five of their rookie-listed players to the senior list.
Bombers football manager Rob Kerr said that both Crowley and Kelly were in "good nick" despite not being a part of an AFL training regime for the last few months, but they had a "big task" ahead of themselves to be match ready by the start of the season against Gold Coast on March 26.
"You could describe them (both) as fitness fanatics so they're in pretty good nick," Kerr told SEN on Thursday morning.
"But obviously being in good nick and then preparing for an AFL season, specificity of training and the like is really important.
"Our strength and conditioning team, led by Justin Crow, are going to have a big task of developing a specialised program for them that'll get them ready.
"It would be great for them to be right to go by round one, but we've got to be realistic about it and if their preparation is such that means round one may not be the best time for them we've got to think about the 22 rounds and how we can get maximum value from those guys and we obviously don't want to put them in a situation where they're risking an injury because we really want them to play as many games as they can."
Kerr said Essendon would try to ensure that as many as seven of their 10 top-up players were experienced to help with the development of the team's youngsters.
"We think that Ryan and James are two players that have been around the game for a long time and will have a fair bit to add to our young group so we're pleased to be able to get a couple of players of that calibre involved," Kerr said.
With All-Australian duo Cale Hooker and Michael Hurley unavailable this season due to suspension, along with Tayte Pears, the retired Dustin Fletcher and Jake Carlisle who joined St Kilda, the Bombers' key position stocks have been ravaged.
Compounding matters for Essendon is that they are struggling to find experienced players to fill those holes on the list.
"The area where we're having difficulty is with your talls," Kerr said.
"Talls are a pretty valuable commodity, so we may end up having to go a little younger when it comes to the talls.
"Most experienced talls who have got real promise are either on an AFL list or have retired through injury or something like that."
Kerr said former Melbourne ruckman Mark Jamar and former Bulldogs tall Ayce Cordy were being considered by Essendon.
If Essendon wanted to retain one of their top-up players beyond season 2016, they would have to do so through the draft as they did with Mitch Brown last year following his cameo as a top-up for the Bombers in the 2015 NAB Challenge.