The 'Deadman', whose 21-year unbeaten Streak at 'Mania came to an end against Lesnar, suffered what the company's website described as a "severe concussion".
After returning backstage following the match, 'Taker was taken to a local hospital in New Orleans and kept in overnight.
A statement read: "WWE.com can confirm that, following last's night historic match with Brock Lesnar, The Undertaker was immediately taken to Ochsner Medical Center.
"After a CT scan and other medical testing, he was diagnosed with a severe concussion and was kept overnight for further evaluation. He was discharged early Monday afternoon."
Elsewhere on the show, Daniel Bryan finally captured the WWE World Heavyweight title after overcoming Triple H in the night's opening bout, before seeing off Batista and Randy Orton in the main event.