The Recreation Ground club face a potential banana skin when they visit amateurs West Hull on Saturday.
Giant killing acts are limited in the rugby league Challenge Cup but they do happen.
And Forster is conscious West Hull were runners-up in last season’s National Conference Premier and champions in 2014.
“I respect their record and what they have achieved, and they will be certainly giving it their best shot on Saturday," Forster said.
“It’s their Cup Final, taking on a semi-professional team, so we know what to expect.
“My main concern is that we go with the right attitude and it will be about how we conduct ourselves on the day.
“I will be speaking to one or two people about West Hull but I’m more concerned on how we perform. We have to show he right attitude in our preparation and during the game."
The Haven player coach was hoping to be recovered enough to lead his side from the front.
Forster had been feeling far from well last week but he went out for the derby clash with Workington, where he bravely put in an 80-minute shift.
“I was certainly feeling it afterwards,” admitted a battered and bruised Forster.
The other main casualty from the 22-6 home defeat by Town was centre Jake Moore who suffered a broken hand.
Forster had several players unavailable for the Town game, hence the decision he and Scott McAvoy made to play.
Forster said: “On another day, myself and Scott wouldn’t have been involved in the game but hopefully we will be able to go again on Saturday and with a few more bodies to choose from."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here