The newly-promoted Bees are currently fifth in the Championship table.
"We have done a lot of dealings in the transfer window and if we bring anyone in, it will be to be a starting player," he told BBC London 94.9.
"The owner is keen if we can find someone. At the moment it will have to be a good player to get in this team."
He added: "If we think we we can improve the group, it will have to be special players."
Brentford are back in the second tier of English football for the first time since 1992-93, having finished second in League One last season.
The west London club brought in 12 new players, three of whom were on loan, over the summer, but McParland says Bees owner Matthew Benham is happy to spend more to strengthen the squad in the new year.
"We've had marvellous support from the owner," McParland added.
"He has got massive plans for the club, with the new stadium, and we have a manager [Mark Warburton] who is fearless and will play young players.
"The owner has a long-term plan for the club and he is heavily involved in the recruitment process.
"If the three of us really like a player and it is going to cost some money, Matthew will look at it and if we can do it, we'll do it."
Brentford sporting director Frank McParland says they will only enter the transfer market in January if "special players" are available.