Queens Park Rangers have conceded 20 goals in the Championship already this season.
The R's have made a poor start to the season, despite beating Bolton Wanderers 4-3 in their latest outing, and the porous nature of their defence has been particularly worrying.
QPR have already conceded 20 times this season, the joint highest amount of any team in England's second tier, and Fer admits that his team need to improve in this respect.
"It's great to go into the break with a win," the Dutch midfielder, who scored against Bolton, said.
"We showed that we can attack well, but there is a lot to improve on. We can't keep conceding the goals we're letting in.
"We have to crack on over the next fortnight, train hard, work on certain aspects of our game, and focus on the next game."
The international break has come at a good time for Chris Ramsey, as it gives him a chance to address some of the issues his side have faced this season.
QPR have not played up to their potential so far this campaign, and they appear to be a team in transition, after a summer of upheaval.
That said, the R's have proven that they can score goals at Championship level and they are still only three points away from the playoff spots as a result of their attacking excellence.
It means that a slight improvement could put them back up into promotion contention, and Ramsey will be hoping that after two weeks on the training ground, his QPR team will be a lot more defensively secure for the rest of the season.