Harrison has suffered an ACL rupture that has required surgery and he will not be able to feature again this season.
And with the 29-year-old set to depart for France to join second division side Provence this summer, his time wearing a Saints shirt has come to a sad end.
But there can be no doubting the immense contribution Harrison has made to the black, green and gold since making his way into the first team in 2012.
He was initially spotted by Dylan Hartley during the 2011 World Cup in New Zealand and then flew over to join the Saints Academy.
Eleven years and 185 appearances later, Harrison has established himself as one of the most influential figures in recent Saints history.
But he will not be able to make one more appearance, instead his final game for the club will be the incredible comeback win against Bath last month.
Speaking at Thursday's media session ahead of Saturday's Gallagher Premiership trip to Saracens, Boyd said: "I'm gutted for anyone who gets a long-term injury because it's a tough place to be, but Tei has been a warrior for this club.
"I don't know how many years he's been here but he's been unbelievably good for the club and I've loved working with him and seeing him play.
"For him to go out like that and finish his playing career with the Saints watching from the sidelines is very frustrating for him, but it's part and parcel of being a professional rugby player.
"Injuries are a part of life, loss of form is a part of life and somebody else's performance when it means you're not being selected is also part of life.
"It can be cruel sometimes."
Saints will also be without tighthead prop Conor Carey for the rest of the campaign after he suffered a serious knee injury in the win against Harlequins at the end of last month.
Boyd said: "Conor Carey blew his knee out only five minutes into the game against Harlequins and he's gone under the knife this week so his season is finished."
Saints lost five players to injury during the clash with Quins, with Carey, Paul Hill, Juarno Augustus, Alex Coles and Fraser Dingwall all forced off.
And Boyd said: "We haven't solved all of those problems but it is what it is at this time of the year.
"You need a full squad but I don't know why it is that you get pockets of problems.
"Last year we'd lost just about all over our looseheads, the year before it was hookers and this year it's loose forwards.
"We're a number of loose forwards down so it's cometh the hour, cometh the man and you've just got to battle on.
"We've solved some issues but not all.
"There are a bunch of guys who are close but probably no cigar.
"Other than Teimana and Conor, everyone else is there or thereabouts but it's still a little bit ropey."
There could be some good news on Ehren Painter, who looked set to be out for the remainder of the season with a bicep injury.
But Boyd says the tighthead prop has a chance of featuring again.
"He may be back," Boyd said.
"He had a bicep rupture and he's getting reasonably close.
"We don't have a game next week so anyone who is reasonably close and we can give another couple of weeks to, we'll probably give them rest.
"In another two weeks (when Saints host Newcastle Falcons in their Premiership final-day fixture), we can hopefully achieve quite a bit."