Strachan (left) watched Maloney leave Celtic for Aston Villa

Strachan had hoped the 23-year-old would remain with the SPL side following protracted negotiations.

But Maloney sealed a �1m switch to the Premiership to team up with former boss Martin O'Neill.

Strachan said: "I was very close to him. But there have only been about four or five people throughout the club's history that you can't replace."

Maloney sealed his switch to Aston Villa with minutes to spare before the January transfer window closed on Wednesday.

Strachan said: "It's disappointing to lose all good players.

"It was disappointing when Roy Keane retired, when Stiliyan Petrov left, when John Hartson moved on, when Chris Sutton left.

"It's more disappointing because Shaun was young and I was very close to him."

O'Neill said he was confident Maloney would have a successful career in the Premiership.

Celtic signed Hearts midfielder Paul Hartley, Inverness Caledonian Thistle goalkeeper Mark Brown and Cameroon full-back Jean-Joel Perrier-Doumbe during the transfer window.