Pompey entertain the Cottagers and Davis knows a win for the home side could end up sending his old side down into the Championship.
Davis climbed all the way into the top flight from the old Third Division during his time with Fulham but with FA Cup final places at stake, he knows there can be no room for sentiment.
“There are no mixed emotions for me because I really hope Fulham stay up, but I have to give 100 per cent for Portsmouth,” he said.
“It is a shame it has come to this situation because we fought so hard to get promoted and I will be gutted if they get relegated.
“All the players I played with have moved on but I know Simon Davies and Paul Konchesky well. It will be horrible if I end up relegating my mates.”
Watford boss Javi Gracia does not think Abdoulaye Doucoure's form will be affected by his omission from France's latest squad.