The Blues sit third in the Premier League with four games left on 65 points, with Arsenal a point behind and Spurs two further back in fifth.
Rafael Benitez's side face three games in six days across two competitions as their marathon campaign draws to a close, starting with a Europa League semi-final second leg against FC Basel.
Lampard believes that a positive result against Spurs at Stamford Bridge next Wednesday will go a long way towards securing a place in next season's Champions League.
He told The Sun: "You could say the game against Manchester United is pivotal, but I think it is really down to the Tottenham game.
"I think it will go to the wire but if we get the right results against United and Tottenham we'll put ourselves in a healthy position.
"The Champions League is the test of the best and the main target, but I want to win the Europa League as well."
The Blues will face champions Manchester United at Old Trafford on Sunday before the crunch encounter with Spurs, led by former Chelsea boss Andre Villas-Boas.