The 34-year-old Australian pace spearhead had figures of 6-56 off 32.3 overs and 4-30 off 18 overs in the second innings in NSW second XI's nine-wicket win over Victoria in Melbourne.
It followed just one Sydney club game last weekend after a seven-month lay-off because of ankle problems.
The NSW selectors will pick their team on Saturday for their final Shield game with Queensland starting next Thursday, when Steve and Mark Waugh will each play what could be their last first-class game.
McGrath seems certain to be included as State selector Dion Bourne said the panel was "enthused with the way he bowled" in Melbourne.
"The longer he bowled, the better he got. He's still got his accuracy and guile and he bowled very well in the first innings," Bourne said on Thursday.
"But in the second innings he stepped up another cog, he was, in my view, better than before he had his injury.
"He seemed to be back to the form of about a year before he had his break with the injury.I truly believe he is 98 percent back to his best and his bowling in the second innings was really, really good. I know Glenn came through the match well, he had no ill effects and he's very fit, he's had this ankle surgery but has maintained the rest of his body in a pretty superb state of fitness."
McGrath will be one of several internationals returning to the NSW line-up with One-day representatives Michael Clarke, Michael Bevan and Brad Haddin returning from Australia's series in Sri Lanka.
Fourth-placed NSW could still make the Shield final if they beat third-placed Queensland outright and competition leaders Victoria do likewise against second-placed Tasmania in Hobart.