The band, who were scheduled to play the Radio 1/NME Stage, have pulled out because frontman Grant Nicholas has contracted laryngitis.
Nicholas said: "I'm absolutely gutted to have to pull out of these shows and my sincere apologies go out to all our fans attending.
"I have an infection and my doctor has diagnosed me with laryngitis, so performing this weekend is not an option. If I did, I'd badly damage my voice.
"We'll miss the ever-brilliant Scottish crowd, especially as they're so up for it, but we're now looking forward to coming back to Glasgow for the 'Generation Freakshow' tour in November."
Tinie Tempah will headline the Radio 1/NME Stage tonight, with Professor Green, Olly Murs and The Temper Trap performing before him.
Snow Patrol, New Order and Florence + the Machine will also play at T In The Park today.
Feeder are due to appear at this year's Reading and Leeds Festivals on August 25 and 26 respectively.
Watch Feeder's video for 'Feeling the Moment' below: