He said: “Nottingham Forest is going down. UP THE BLADES!!!
Delighted Blades fans recalled how the musician famously sang the club’s Greasy Chip Butty song on stage at a Chili Peppers Sheffield gig in 2011, and took to Twitter to comment Flea’s remarks.
Danny said on Twitter: “Was at Sheffield in 2011 when he sang the greasy chip butty song live with RHCP. Was great!
pRaYiNgMaNtIs added: “100% Flea Up the Blades.”
Stevo said: “I was there when u sang it at Sheffield Arena, my Wednesday pal who got me the tickets wasn't so impressed.”
The Red Hot Chili Peppers’ latest album, Unlimited Love, has been an international number one, and they are on tour this summer to promote it.
The first leg of the Blades’ play off clash with Forest will take place at Bramall Lane on Saturday, with the return fixture at the City Ground three days later.
Whoever progresses over the two-legged tie will play either Huddersfield Town or Luton in the final at Wembley on Sunday 29 May.
United have failed to win promotion via the play-offs in no fewer than eight attempts, although manager Paul Heckingbottom has previously tasted success, having twice won promotion via the end-of-season contest as a player and was promoted with Barnsley as caretaker manager.