The Fulham boss started the window calling for early arrivals to aid the club's fight against relegation, with a striker top of the list for new recruits.
Aleksandar Mitrovic has been in desperate form this season, while Ivan Cavaliero has struggled when it comes to finishing in his place.
However, with a bloated squad that Fulham are struggling to cut down, Parker admits new faces are unlikely.
"It is going to be difficult for us to be honest," said Parker.
"We understand where we need to improve, we’re a team that have just come up from the Championship and the void to the teams who are established is huge.
"You need to try and be competitive, need to evolve and bring players in. At the same time the balance of expenditure and a realism of where you are is needed.
"At this moment in time it is going to be a challenge for us. If that is the case I understand and we all understand the situation."
One of the fringe players who will move on, however, is Stefan Johansen. The midfielder, left out of the Premier League squad this season, is set to cross west London to join Queens Park Rangers.
"Stefan will go there to play some games and get some football. I am expecting that to go through," added Parker.
"It is clear that the squad is quite big in terms of numbers. There is the option to some to go and get some game time."