Suso's free kick cancelled out an early Giovani Lo Celso strike in Seville.
“It's good to play well, but there is some bitterness. Our wing-backs were too deep in the first half and never pushed up, so we did better after moving to 3-4-3," Gattuso told Sky Sport Italia.
“We were timorous early on and conceded a goal early through our error, but the lads deserve credit because they fought back and showed character to get a result in a difficult arena.
“Once again tomorrow, we'll have to count to see how many players we actually have left."
Gattuso added: “Having a player like Tiemoue Bakayoko means you don't always have to play from the back, because he can go up there and knock on a long ball. We had one striker today, Patrick Cutrone, and didn't give him the right service, but we're learning with this system and hope to improve it with more experience.
“The easiest thing during this period was to seek alibis, saying we had injuries because we worked too hard or not enough, that the players weren't following my orders, etc. We resisted that and always work hard, even if I might wind them up."