Aaron Heppell, the younger brother of Essendon star Dyson, is one of 13 players signed by the Bombers on short-term contracts ahead of the NAB Challenge. 

While the older Heppell underwent minor knee surgery this week, his brother is in the mix to play for the club as it opens its pre-season campaign against St Kilda on Saturday at Morwell.

The club on Wednesday announced its batch of players who have been approved by the AFL to play during the NAB Challenge, with nine of the 13 already having AFL experience.

Mitch Brown (Geelong), Mitch Clisby and James Magner (Melbourne), Clint Jones (St Kilda), Jared Petrenko (Adelaide), and James Polkinghorne and Sam Michael (Brisbane Lions) were among the first group of delisted players signed as top-ups.

But the club will also call on six more players from its VFL list, including former Essendon rookie Marcus Marigliani and Jordan Schroder, who played five games for Geelong.

Medium tall Josh Freezer, talented flanker Anthony McDonald-Tipungwati, ruckman Sam Tagliabue and Heppell, a midfielder who knows his way around contests, round out the squad.

Heppell was overlooked for the NAB AFL Draft in 2013 after playing with the Gippsland Power and Vic Country, and played nine games with the Bombers' VFL team last season. 

Essendon initially thought it may need more than 20 fill-in players to replace the 25 Bombers unavailable for the NAB Challenge.

Every player who was on the club's list in 2012 will not play in the pre-season competition to protect the names of the 17 or so players handed infraction notices by ASADA and under provisional suspensions.