The Nerazzurri missed a penalty for the second Serie A match in a row as they failed to build on their 2-0 victory against Chievo last week.
Sunday's draw leaves Inter's European hopes in further danger ahead of Roma's match against Genoa on Monday, with Catania catching the San Siro outfit after a 1-0 victory against Lazio.
"We are disappointed because we could not win the match despite our commitment," Ranieri told Sky Sport Italia.
"This has not been an easy season, we know it, but I cannot blame any of this on my players.
"We have to take one match at a time without making long-term objectives.
"We have got to continue with this professional attitude without talking about third place or any other objectives."
When asked about his tactical choices, Ranieri insisted he completely trusts his 4-4-2 system.
"This is our squad and I have to try to do my best with this group, without thinking about what happened in the market," he added.
"This is the best team that I can field. Thiago Motta? If a player wants to leave, you cannot keep him."
Atalanta also had penalty claims late in the match, when Manolo Gabbiadini appeared to have been brought down by Lucio inside the Inter box.
"You could award a penalty for that, it depends on the referee," Ranieri said. "Lucio only reached the ball after making contact with the player.
"We have not been awarded penalties which were even clearer."