Murphy looks set to play his last game for the club in Wednesday's Scottish Premier League clash at Celtic Park after holding talks with npower League One promotion hopefuls Sheffield United.
Murphy rejected a move to Blackpool on the final day of last January's transfer window in order to help Motherwell seal a slot in the Champions League qualifiers but his salute to the Fir Park fans following Saturday's 2-2 draw with Kilmarnock looked like a farewell.
Manager Stuart McCall expects the 23-year-old to move on after the Celtic Park clash and Humphrey feels his team-mate will go on to bigger things.
The Jamaica international said: "I'm sure it will be emotional for him and I'm sure it was emotional for his last home game.
"But he will be looking forward to it and will want to leave on a high.
"He has been terrific for the four years that I have been here. I think it's a long time overdue. He has done terrifically well and I wish him all the best.
"Obviously we will see him for the game on Wednesday but he deserves everything he gets because he has been fantastic."
Murphy has scored nine goals in his last 13 games from midfield and Humphrey believes his friend can improve further.
"I think he can be unbelievable," the former Shrewsbury winger said.
"He has always had the right head on him to do well and I think he can go on to big things."
Murphy has a difficult game to make a farewell impression with Motherwell having scored just three times in their last 12 visits to Celtic Park, although that meagre return has yielded four points.
But they sit just six points behind Celtic, who lost 1-0 at Hibernian on Saturday following earlier defeats by St Johnstone, Kilmarnock and Inverness this season.
Humphrey said: "It's always a tough place to go and you can see past results haven't been the best but form-wise we have been doing really well.
"I'm looking forward to going there and giving them a right good game.
"Obviously they lost at the weekend and won't be happy but I'm sure if our heads are right and we play the way we can do, we can give them a good game.
"We have not been in awe of them, they just have great players and bigger budgets to buy players.
"So we have to just go there and try and do what the manager wants us to do.
"We need to redeem ourselves the way we have played against them in the past and see if we can get a good result against them."