Reader also confirmed that 2020 Melbourne premiership-winning centre Brenko Lee had been released from the final year of his Dolphins contract next year so he can explore lucrative options in Super League.
Dolphins officials held their breath in the second half of the Bulldogs' 34-30 loss to the Gold Coast on Sunday when Averillo left the field in the 65th minute, with initial concerns it could be an ACL injury.
The speedy and skilful Averillo will join the Dolphins next year to add strike power to their backline.
"Jake got the results of his scans through last night and it is a PCL (posterior cruciate ligament) injury and he will be ready to go for the start of pre-season," Reader told AAP.
"We spoke to the Bulldogs straight away on the day and the good news came later about Jake's scans.
"I was watching my young fella playing touch on Sunday and when I got in my car I had 10 messages from mates saying, 'Jake has done his ACL'.
"Fortunately we had spoken to the Bulldogs staff straight after the game and they were confident it would be nothing major. That has now been confirmed."
Averillo will be on deck to partner England international Herbie Farnworth, the gun Brisbane Broncos centre, at the Dolphins next year.
It makes more sense of the decision to let 2020 Queensland State of Origin hero Lee go.
Lee was a member of the Maroons side in the 2020 Origin series decider in a 2-1 series win for the Wayne Bennett-coached side.
Bennett lured the 27-year-old to the Dolphins from Brisbane and he played just 13 games in 2023, due mainly to injury.
Reader said Lee's early-season form and performance in the 28-18 win over Sydney Roosters in the club's inaugural match was a highlight.
"We have mutually agreed with Brenko's management to release him from the final year of his contract so he can explore other opportunities in the UK," Reader said.
"Brenko will always be valued as a foundation player. He played in that first game against the Roosters and was an important part of setting up that first stanza of the club and how the team was going to play.
"Whatever way you look at it Brenko will forever be Dolphins No.4 that got the club on its way."
