Liverpool boss Jurgen Klopp spoke to former Red Marko Grujic before signing Luis Diaz.
Grujic was the German's first signing back in January 2016 and had a host of loan spells away before heading to Porto.
He's in his second year at the Portuguese club meaning he's spent 18 months alongside Diaz.
Those at Anfield spoke to Grujic to get a character reference before pursuing the Colombian's signature, reports the Athletic.
Liverpool and Porto met in the Champions League earlier this season, which allowed the former Red to reminisce about old times.
At that point several people asked Grujic what Diaz was like as their interest begun to mount.
“Some people from the club asked me what Luis was like as a person,” said the Serbian midfielder.
Will Sadio Mane start ahead of Luis Diaz? Have your say in the comments!
“They asked me about his behaviour off the field. I told them that he was a great guy who would fit easily into any group of lads.
"I also spoke a bit with Luis about Liverpool. Luis was very happy that a club like Liverpool were interested in him.”
The Reds, known for their shrewd recruitment, were planning to pursue Diaz in the summer.
However Tottenham made moves to sign the winger in January which forced Liverpool to act and sign him.
A £50m deal was agreed with Diaz already making his debut for the Merseyside outfit.
He will push Sadio Mane and Mo Salah for a starting role going forward with the Reds still eyeing all four trophies this season.
Diaz's move came whilst he was on international duty with Liverpool staff having to jet over to South America.
It meant the player was unable to have a proper farewell with his Porto teammates but Grujic has given the new Liverpool man a glowing review.
He added: “As players, we didn’t expect it to happen. It all happened so fast after Luis went away with the national team so we didn’t get to say a proper goodbye to him.
“We will miss him so much because he’s a great player. He scored a lot of important goals for us.
"Any squad losing someone of his calibre would miss him because he has the quality to make a big difference in games. He’s capable of changing games in the space of just one second.”
He also added: “Luis has been unstoppable this season. He produced some crazy things for us in the final third."
Grujic was also quizzed on advice he would pass on: “It’s maybe a bit more difficult in the Premier League but he will adapt quite well, I’m sure about that. He has the physical attributes.
"He’s strong and his pace and acceleration are incredible. He has unbelievably quick feet and that gives him the quality to play against any defender."
