With the Blues presently serving a transfer ban, Pulisic is the main new marking at Chelsea this summer, after his £58million transfer from Borussia Dortmund was agreed in January.
Lampard selected against giving Pulisic a begin in his first competitive match accountable for the club on Sunday, picking rather to field Pedro and Ross Barkley in the wide regions, with England youth Mason Mount in help of forward Tammy Abraham.
Pulisic was in the end presented in the 58th minute when he replaced Barkley.
Chelsea were at that point 1-0 down at that stage, on account of a first half penalty from Marcus Rashford.
Pulisic had brief period to have an effect on the game before United multiplied their lead through Anthony Martial on 66 minutes.
Further breakaway goals from Rashford and debutant Daniel James, added more hopelessness to Lampard.
Talking after the game, Lampard uncovered his purposes for his group choice and his arrangements for Pulisic going ahead.
“Christian Pulisic is 20 years old and he’s come across from Dortmund. He will be a fantastic player for the club. He has got great ability. You saw little moments with his acceleration on the ball.
“But I have also got other options in midfield and in those areas, and I don’t want to stick Christian straight into the fire without trying to help him along the way. It was one of those games where I felt it was better to start with Ross [Barkley] and Mason [Mount], who have been very strong in pre-season, and bring Christian on.
“If the game had carried on at 1-0, or we were back in the game as we should have been, he would have been a great injection. In the end, it was difficult for him because the game went quickly away from us,” Lampard told reporters.