Two of those matches are away from home and they face Chelsea at Stamford Bridge on the final day.
Caretaker boss Gray said: "For us to stay up I think we have to win the three matches and that has not happened in sequence this season. It is going to be extremely difficult. I felt this (Portsmouth) was a fixture we had to win.
"You have to be realistic in football and we know how difficult it will be now. We gave away a couple of sloppy goals and lacked the quality to break Portsmouth down.
"But where there are points to play for we have to continue to work hard in the hope of getting results. We have not performed well enough, it’s quite simple, but the boys worked hard to the end of the game."
Gray added: "If you win the league, it is because you deserved to win it. If you play 38 games and you are in the bottom three you deserve to be relegated."
Caretaker boss Gray said: "For us to stay up I think we have to win the three matches and that has not happened in sequence this season. It is going to be extremely difficult. I felt this (Portsmouth) was a fixture we had to win.
"You have to be realistic in football and we know how difficult it will be now. We gave away a couple of sloppy goals and lacked the quality to break Portsmouth down.
"But where there are points to play for we have to continue to work hard in the hope of getting results. We have not performed well enough, it’s quite simple, but the boys worked hard to the end of the game."
Gray added: "If you win the league, it is because you deserved to win it. If you play 38 games and you are in the bottom three you deserve to be relegated."