Stewart Donald asked Sunderland fans to stay united after a disappointing end to the League One season.
The Black Cats have won just once in seven, their 2-1 defeat to Southend United on Saturday meaning they finished the season in fifth place and with back-to-back defeats.
They will now face Portsmouth in the play-off semi finals.
A win at Roots Hall would have pushed them into third and set up a clash with Doncaster Rovers, who now face Charlton Athletic.
Donald tweeted: "Sunderland AFC fans. Your support has been sensational. You have wanted to believe in us and have been inspirational. I appreciate a lot are frustrated with the p/offs. We can though still do this. We can reflect later but our best chance is with your backing - together please."
The first leg will be played at the Stadium of Light next Saturday night.
Tickets start at £20 for adults, £17.50 for over-65s, £12,50 for under-22s and £7.50 for under-16s.
Donald told supporters he had hoped to price them cheaper but was unable to.
He said: "The rules state that in the absence of clubs being able to agree play off ticket price that standard matchday pricing will be charged. All clubs are asked for their proposed pricing and match day prices was not our recommendation."