The striker made his second debut for the club in Saturday’s goalless draw against Brighton and Hove Albion at St James’s Park.
Carroll, signed on transfer deadline day last month as a free agent, came off the bench and helped Steve Bruce’s side take the game to their visitors in the dying minutes.
Lascelles knows from experience just how tough an opponent Carroll can be, having played against him when he was at West Ham United.
"He can have a huge impact here,” said Lascelles, United’s captain. “I've played against him when he was at West Ham.
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“If he's coming off the bench for the last 20 minutes centre-halves are going to have a tough time. Not necessarily because he's going to score, but he's going to draw bodies towards him and make room and time for others. He could be a real problem.”
Bruce said ahead of the Brighton game that Carroll’s return from ankle surgery had raised the levels in training.
"Yes, just his presence (raised the levels),” said Lascelles. “He's a well-respected player, and he adds so much to the changing room, which is important. When I saw him running onto the pitch I thought 'come on, let's go for it'. He gave us all a boost.”
Carroll was sold to Liverpool by Newcastle for £35million in January 2011.
"He's a real leader,” said Lascelles. “He knows he's got unfinished business here. He was here four years, and he'll be wanting to play a lot of minutes this season to help us as much as he can. He's a great signing.”
There were some boos at the final whistle from frustrated fans, who had witnessed their team struggled to get the ball from Brighton.
The result left the club with five points from six Premier League games.
"This is a game we definitely wanted to win,” said Lascelles. “We've played three of the top clubs, and we'd have been really happy with the points if we'd won (against Brighton). We've got players coming back from injury, and it's a marathon not a sprint.”