The Bhoys were looking to start their Europa League group stage campaign on a positive note and stunned Real Betis by going 2-0 up in Seville.
Albian Ajeti struck in the 13th minute before Josip Juranovic scored from the penalty spot 14 minutes later to leave the Spaniards reeling.
Jota missed a good chance to make it 3-0 and Celtic paid the price when Real Betis scored in the 32nd and 34th minutes to make sure the sides went in locked at 2-2 at the break.
Manuel Pellegrini’s men then netted twice in the second period, being 4-2 up by the 53rd minute.
Celtic ensured a nervy finish for the hosts though when Anthony Ralston headed home with three minutes left, but it ended 4-3 to Real Betis.
McManus admits Celtic were shaky at the back, but the former top flight attacker praised the Bhoys’ approach to the game.
“Celtic had a go and got beat from a very talented and expensive side in Betis. No disgrace”, he wrote on Twitter.
“Go there and score 3 must be a huge positive.
“Yes poor at the back at times but rather watch that type of performance than going and stringing 10 men across the 18 yard box and still getting beat”, McManus added.
Celtic are third in Group G after the loss in Spain, with the other game in the group seeing Bayer Leverkusen beat Ferencvaros 2-1 at the BayArena.