The Reds defender is enduring a furious backlash from fans after it emerged this week that he is committing to a free transfer to Real Madrid at the end of the season.
Souness wrote for the Daily Mail: "I understand the frustration of Liverpool supporters towards Trent Alexander-Arnold over his decision to join Real Madrid but I don't think they can be too critical.
"I'm not sure whether the backlash is more because Liverpool won't be getting a substantial fee or just that Trent has chosen to leave.
"The timing of the news is unfortunate but that leak would not have come from Trent or his team. There is zero benefit to him or Liverpool in this coming out at this time, with a league title still to be won.
"Whatever the reasoning, the flak that may come his way in the remaining months will be nothing he can't handle. You don't play for a club like Liverpool with a poor temperament so he will cope with the criticism.
"He has given good service. He has been at the club for 20 years, he has won six trophies and what looks like becoming two Premier League titles, now he fancies another challenge. Like any ambitious young man, should we begrudge him that?
"Not to mention, in Conor Bradley, Liverpool have a ready-made replacement who has all the hallmarks of becoming a top, top player.
"There are no obvious replacements for Mohamed Salah or Virgil van Dijk, so Liverpool supporters can at least take solace that Bradley is already in the building."