Trippier, 28, has come through the ranks of the Manchester City Academy and has been made available as Tottenham has a team off to make room for signings.
Both Napoli and Manchester United and Napoli are interested in Trippier, who helped Tottenham reach a Champions League semi-final and third place in the Premier League.
Last summer he was part of the England team that reached a semi-final of the World Cup. However, he has struggled to find his best form for much of this campaign.
Tottenham chairman Daniel Levy is known for making a tough bargain and it will not be easy for clubs to get Trippier for less than the prize.
Manchester United wants to experience an exciting summer with coach Ole Gunnar Solskjaer.
The defense will be a priority for Solskjaer with United who urgently needs new players.
And the Norwegian has admitted that he already knows what kind of player it is.
He said, "We were looking for scouts to search the planet for good footballers, and we're going to hire players we think are the right ones, and I'll get the players.
"I talked to the club, we know we have to be realistic and have a job to do. There is no quick fix.
"It's not like buying seven players, and we're in the right form, we need to go step by step and signatures are made, but we also have to think about players.
"Sit down, have a preseason, I can not wait.
"There will be a few additions, the players will have to come back and know what is expected of them, and take over on vacation, and it will be great to see who comes back."
United has been associated with a number of other stars, including people like Kalidou Koulibaly, Aaron Wan-Bissaka and Jadon Sancho, who have managed to be on their radar.
It could also come to clashes with Paul Pogba, who is believed to be on Real Madrid's radar.
Securing the Champions League football could be the key to Solskjaer not signing players this summer.
The Red Devils are currently sixth in the Premier League table, two points less than the fourth-placed Arsenal.
Solskjaer's team will go to Everton in the next match on Sunday (13.30) before being welcomed in Manchester City on Wednesday.