The Potters are second from bottom of the table, six points from a position of safety, and their head coach believes that they need to win three of their five remaining matches to stay up, starting with Monday night's trip to West Ham United.
"I don't think we can afford to lose it. I still think we've got to win three games. There will still be a lot of twists and turns. We're going into the game confident," Lambert told BBC Sport.
"I know it's a difficult game - it's a massive game for them as well. If we win, then it pulls them right back in it."
Lambert took over the Stoke hotseat in January following the sacking of Mark Hughes.