The Jags boss yesterday agreed to become the manager of Dundee United, bringing the curtain down on an impressive 18-month stint in Maryhill.
With the club second in the Irn-Bru First Divisions standings and in the final of the Ramsdens Cup, the loss of McNamara and assistant Simon Donnelly could not have come at a worse time.
Club captain Alan Archibald has been placed in interim charge and McParland insists the overhaul need not prove too disruptive to the Jags' cause.
He said: "They are sitting very nicely in the league and it would be a terrific achievement if they could get up this season.
"You generally find that players are quite receptive to new managers. It might not be to their advantage right away, but you have got to give the new boss time to show what he can do and get his ideas across.
"I have not come across a group of players that didn't get stuck in for a new manager. They have to because he is the one picking the team the next week.
"Jackie's exit may not have come at the right time, but they still have a good squad and good chance of winning promotion.
"The players have done a great job to get where they are and it would be a pity to see that lost because Jackie has moved on.
"If Alan is there and is capable of doing the job then why go looking elsewhere and bring in someone you maybe don't know as much about? That is how I got the job.
"Anyone going in will have good players to work with and hopefully they can continue the good work Jackie started."
In the 18 months since McNamara replaced Ian McCall in the Firhill hotseat, the former Scotland defender has emerged as one of the brightest young managers in the country.
He takes over on Tayside from Peter Houston and McParland has backed the 39-year-old for more success in the SPL.
He said: "Jackie will do well at Dundee United. It will take him some time to settle in, but he has a good head on his shoulders."
Thistle have announced that Scott Paterson will assist Archie as interim assistant manager.
A club statement said: "Whilst bitterly disappointed we had no option but to accept this and now need to move on.
"Our ambition at the start of the season was to win promotion up to the SPL and that's not changed."