Valencia were level just eight minutes later, however, when Dani Parejo stroked home with his right foot following some sloppy play from Leicester in a defensive position.
Maddison continued to impress for the Foxes and set up another chance for Iheanacho in the 31st minute, but the Nigerian saw his shot saved by Jaume Domenech.
Darnell Johnson had a super chance to send Leicester ahead early in the second period, but the young defender looped his header over the crossbar from close range.
Fousseni Diabate was next to come close for the Foxes in the 67th minute, but the attacker was somehow denied by Neto from close range as the two teams remained level at 1-1 heading for the final 20 minutes.
Leicester substitute Josh Gordon twice tested Neto in the latter stages of the match, but neither team could find a second as the spoils were shared at the King Power Stadium.
Leicester's final pre-season match is against Lille this weekend before opening the 2018-19 Premier League season away to Manchester United on August 10.
Valencia, meanwhile, still have Everton and Bayer Leverkusen to tackle before beginning their La Liga campaign at home to Atletico Madrid on August 20.
LEICESTER: Schmeichel, Ricardo (Silva 46'), Benalouane (Johnson 46'), Morgan (Gordon 63'), Chilwell (Fuchs 63'), Albrighton (Ndukwu 63'), Iborra (Choudhury 63'), Ndidi (Amartey 46'), Diabate (Thomas 75'), Iheanacho (Elder 46'), Maddison (Knight 63')
VALENCIA FIRST-HALF XI: Domenech, Latorre, Murillo, Vezo, Piccini, Torres, Parejo, Medran, Kondogbia, Zaza, Rodrigo
VALENCIA SECOND-HALF XI: Neto, Piccini (Montoya 64'), Diakhaby, Murillo (Garay 72'), Gaya, Ferran, Parejo (Soler 64'), Kondogbia (Jordi 72'), Wass, Zaza (Lee 72'), Mina