Twenty-two-year-old Dieng, who is of Senegalese descent, has been a regular for Swiss side Grasshoppers B in recent seasons, as well as spending time on loan at FC Grechen, for whom he made his professional debut at the age of 17 in November 2012.
In August 2014, he was the substitute keeper as Grasshoppers played Lille in the Champions League.
He moved to MSV Duisburg, but following their relegation to B3 the German team did not retain his services for 2016/17.
His arrival at QPR in August 2017 coincided with an injury to goalkeeper Conor Hudnott.
He has been a regular in the R`s over under-23 side.
The Hawks have also signed midfielder Simon Mensah on non-contract terms.
The 26-year-old numbers East Grinstead Town, Ware, Grays Athletic, Whyteleafe, Chipstead, Merstham and Carshalton Athletic amongst his former clubs.