Five new players have arrived at the Reebok Stadium this summer but the manager had hoped to strengthen his squad further by bringing Arsenal midfielder Jack Wilshere back for another loan spell after his successful stint with Wanderers in 2009-10.
"I'm very old-fashioned in many ways and I'm from the old school - there really shouldn't be a transfer window," Coyle said.
A similar deal for Manchester United's Tom Cleverley, has not materialised yet and it looks unlikely Bolton will be doing any more business before the summer window slams shut on Tuesday - leaving Coyle questioning why trade is no longer unrestricted.
He added: "I can understand why people brought it in, but for me, the old-fashioned system, where if you had two or three injuries you would go and buy a player if possible - I don't see what is wrong with that.''
Wanderers contacted United about Cleverley earlier this summer but his manager Sir Alex Ferguson has since indicated that he wants the 21-year-old midfielder to stay at Old Trafford.
"I am loath to speak about other teams' players, I always am, but Tom Cleverley is a terrific player," said Coyle.
"He is a very talented young player. We made an enquiry before Manchester United went (on a pre-season tour) to America regarding Tom coming on loan, and Sir Alex said at that time that he would think about it.
"They came back from America, the lad had been terrific on the tour and they decided they would hold onto him, which I totally understand.
"If that changes between now and Tuesday, that is a different situation. As it is, I've not heard that to be the case, but if it changes then I will let you know."
Source: PA
Source: PA