Pakistan opener Sharjeel had been due to appear for Leicestershire in this year's NatWest T20 Blast before he was provisionally suspended during the PSL for alleged breaches of the PCB's anti-corruption code. A tribunal has been formed to examine the case against Sharjeel and Khalid Latif but could take up to three months from the date of the players' suspension to have its first hearing.
The county said in a statement: "The contractual status of Sharjeel Khan is a private matter between Leicestershire CCC and the player, and so unfortunately it is not something that we are able to comment on at this stage."
Ronchi, who has previously played county cricket for Warwickshire and Somerset, will instead join Clint McKay as one of Leicestershire's two overseas signings. He is expected to be available for the whole of the Blast.
"I am delighted to have signed with Leicestershire Foxes for the NatWest T20 Blast," Ronchi said. "I love playing county cricket and can't wait to get started with my new team-mates. It seems like an exciting time at the club with a few personnel changes and talented additions to the squad. I hope I can make a difference both on and off the field and contribute to a successful campaign."
Wicketkeeper-batsman Ronchi has a T20 strike rate of 141.89 from 114 matches. He has played all three formats for New Zealand (having been initially capped for Australia) and is particularly experienced in white-ball internationals, featuring in every match of New Zealand's run to the 2015 World Cup final.
Leicestershire's head coach, Pierre de Bruyn, said: "We're delighted to sign Luke, who will offer power and dynamism to our batting line-up. He has played a lot of games around the world and his experience in the shortest format of the game will also help our youngsters.
"We are determined to improve in white-ball cricket in 2017 and Luke will help us to do that in NatWest T20 Blast. Luke has played for a very good New Zealand side over the last few years and we are excited about him joining us in July."