Context : It is thought that fossil systems are relics of structure formation in the primitive Universe .
They are galaxy aggregations that have assembled their mass at high redshift with few or no subsequent accretion .
Observationally these systems are selected by large magnitude gaps between their 1st and 2nd ranked galaxies ( \Delta m _ { 12 } ) .
Nevertheless , there is still debate over whether or not this observational criterium selects dynamically evolved ancient systems .

Aims : We have studied the properties of the nearby fossil group RXJ075243.6+455653 in order to understand the mass assembly of this system .

Methods : Deep spectroscopic observations allow us to construct the galaxy luminosity function ( LF ) of RXJ075243.6+455653 down to M _ { r } ^ { * } +6 .
The analysis of the faint-end of the LF in groups and clusters provides valuable information about the mass assembly of the system .
In addition , we have analyzed the nearby large-scale structure around this group .

Results : We identified 26 group members within r _ { 200 } \sim 0.96 Mpc .
These galaxies are located at V _ { c } = 15551 \pm 65 km s ^ { -1 } and have a velocity dispersion of \sigma _ { c } = 333 \pm 46 km s ^ { -1 } .
The X-ray luminosity of the group is L _ { X } = 2.2 \times 10 ^ { 43 } h _ { 70 } ^ { -2 } erg s ^ { -1 } , resulting in a mass of M = 4.2 \times 10 ^ { 13 } h _ { 70 } ^ { -1 } M _ { \odot } within 0.5 r _ { 200 } .
The group has \Delta m _ { 12 } = 2.1 within 0.5 r _ { 200 } , confirming the fossil nature of this system .
RXJ075243.6+455653 has a central brightest group galaxy ( BGG ) with M _ { r } = -22.67 , one of the faintest BGGs observed in fossil systems .
The LF of the group shows a flat faint-end slope ( \alpha = -1.08 \pm 0.33 ) .
This low density of dwarf galaxies is confirmed by the low value of the dwarf-to-giant ratio ( DGR = 0.99 \pm 0.49 ) for this system .
Both the lack of dwarf galaxies and the low luminosity of the BGG suggests that RXJ075243.6+455653 still has to accrete mass from its nearby environment .
This mass accretion will be achieved because it is the dominant structure of a rich environment formed by several groups of galaxies ( 15 ) within \sim 7 Mpc from the group center and with \pm 1000 km s ^ { -1 } .

Conclusions : RXJ075243.6+455653 is a group of galaxies that has not yet completed the process of its mass assembly .
This new mass accretion will change the fossil state of the group .
This group is an example of a galaxy aggregation selected by a large magnitude gap but still in the process of the accretion of its mass .