With Dirksen ruled out and a number of players away on international duty, head coach Steve Tandy is without a number of his key players.
Andrew Bishop makes his 181st Ospreys appearance, setting a new record for the region while Owen Williams makes his RaboDirect PRO12 debut in the front row.
"This is the first of two big PRO12 games over the next couple of weeks that will really test us," said Tandy.
"Edinburgh away and then Cardiff Blues at home are always tough games and there's no doubt that we are going to have to show plenty of spirit, commitment and desire on and off the pitch if we are going to get what we want from these matches.
"There's a lot of responsibility on some young shoulders during international periods and it's been pleasing to see players stepping up to the mark and really taking their chances.
"What is equally important to us is the input of senior guys like Duncan, Bearman, Gough and Fussell.
"We've kept hold of a group of experienced players who have the right attitude, knowing that we can mould younger players around them."
Two of these younger players are Nicky Thomas and Sam Davies who will both make their RaboDirect PRO12 debuts if they come off the bench.
"International commitments and injuries mean that our resources are being pushed to the limit but there's a great spirit in the group going into this game," added Tandy.
"Like us, Edinburgh will be hit by national call-ups as well but I think that makes these periods all the more exciting. We get to see what strength in depth there is out there, we unearth a few hidden gems, and we get to see some young Ospreys making their mark.
"We've got some boys involved who have come through the age-grade system but we've also had to dig deep into the Premiership as well, and it's a great opportunity for those guys."