The Shrews' record signing underwent the operation following his side's play-off final defeat to Gillingham in May and is due back in training at the back end of July.
Simpson told BBC Radio Shropshire: "Grant has a bit of swelling, but he's doing well. He's working with the club's physios and he's on target."
Winger Chris Humphrey, still mulling over whether to sign a new contract with the League Two outfit, is recovering following a double hernia operation and Shane Cansdell-Sherriff is making good progress after undergoing ankle surgery at the end of May.
Simpson added: "Chris is up to half to three-quarter pace when he's jogging and should be back on 1 July."