The Tigers' skipper and top scorer has been missing for the last two games after straining a calf muscle against Wolves and his absence has clearly been felt with Steve Bruce's men goalless in their previous three outings.
Hull, currently in second, only hold a slender one-point advantage over Watford going into the final round of fixtures but, even with the ultimate prize riding on the outcome of their clash with the division's champions, Bruce insists he will not risk Koren unless he proves his fitness at Friday's training session.
"He's 50-50," Bruce said. "We'll see how he is but I've just seen the best player in the world (Lionel Messi) last week play not fit and it's difficult. So unless he's 100 per cent it will be a big gamble for me to put him in the starting XI."
The Tigers' options are depleted further as Egyptian striker Gedo, a mid-season revelation, will play no part due to an ongoing foot problem which Bruce suggested could need an operation.
Forward Matty Fryatt, who has not played 90 minutes since August due to an Achilles injury, is expected to start in tandem with George Boyd.