Bhuvneshwar Kumar had shared the new ball with Jasprit Bumrah until the swing bowler suffered a hamstring injury in India's comprehensive victory against Pakistan.
Drafted into the playing XI, Shami sealed India's narrow victory against Afghanistan with the tournament's first hat-trick in Southampton on Saturday.
A fit-again Kumar was back in the nets ahead of the clash against West Indies and Arun admitted the team would have to make a difficult choice at Old Trafford.
"Bhuvneshwar's injury is not of any great concern. It is just a niggle, which we didn't want to take a chance," the former test bowler told reporters on Wednesday.
"And it was also an opportunity for us to plug Shami into the games. But the fact he's done exceptionally well augurs well for us, it's an embarrassment of riches.
"We'd take a call as per the conditions, but Bhuvi has done exceptionally well, so I think it's a pretty good headache to have."
Arun was also pleased with all-rounder Hardik Pandya's evolution as a reliable fifth bowler who could be trusted to bowl his full quota, something not many were sure he could a couple of years back.
"It was a big challenge for him to bowl those 10 overs, and he realised that to be able to bowl those 10 overs 'I need to develop a certain armoury in my bowling'.
"And that's what he's worked on. He's worked on his slow balls, his slow bounces also, and he's also worked on perfecting his bouncers.
"All these put together have given him the confidence to go through those 10 overs."
Bumrah, the top ranked ODI bowler, leads India's formidable pace attack while the two-time champions have a potent slow bowling attack comprising the wrist-spin duo of Kuldeep Yadav and Yuzvendra Chahal.
They do not have a left-arm quick in their ranks though but Arun said the batsmen were prepared to face the likes of Sheldon Cottrell on Thursday.
"We have Khaleel (Ahmed) with us as our net bowler. And we also we have a throw-down specialist who is particularly a left-hander.
"So I think we have enough practise of the left-arm bowling as of now."
West Indies have slim chances of reaching the semi-finals after just one win from six matches and they will need their power-packed batting order to fire against an unbeaten India.
Arun said his bowlers were ready for the likes of Chris Gayle and Carlos Brathwaite.
"It's a big challenge for the bowlers -- especially when they come after you," Arun said.
"But whenever batsmen come after you, if you're willing to look at it deeply, there is a chance in it for the bowlers, and I think that's what the bowlers would be looking to do."
(Reporting by Amlan Chakraborty in Manchester; editing by Pritha Sarkar)
