Schalke conceded six against Real Madrid in the first leg of their UEFA Champions League last 16 tie before losing 5-1 to Bundesliga leaders Bayern Munich last Saturday.
Keller has urged his players to forget about the past, learn from their mistakes and start looking forward.
Hoffenheim travel to the Veltins Arena this weekend and victory for Schalke could see them rise above Bayer Leverkusen into third.
"We have to banish the negative thoughts from our head," Keller said on Friday. "After the Munich game we went over the mistakes in great detail.
"I've spent a lot of time talking to the younger players and pinpointed their strengths.
"We have to look forward now and give the right response against Hoffenheim."
Midfielder Roman Neustadter echoed Keller's comments and acknowledged the heavy defeats exposed some of the weak spots in Schalke's squad.
"We messed up as a team," he admitted. "Both sides (Bayern Munich and Real Madrid) exposed our limitations.
"There's still a chasm between the world-class teams and us.
"We know how to interpret the results, but we also know what we did wrong.
"We have to draw a line under the games and learn from them."
