Richardson is keen to further bolster his squad

Defender Hartley and striker Dowson, both 19, are expected to make their debuts for the Spireites against Brentford this weekend.

Chesterfield boss Lee Richardson told his club's website: "We are grateful to Sunderland manager Roy Keane for loaning out these two players.

"They will help provide some healthy competition for places in the squad."

Richardson is also hoping to add other players - including an experienced centre-back - to his squad.

He said: "We are determined to get our man, but attempts to supplement the squad of a League Two side can be frustrating.

"We have no control over the timing of when the right players become available and it's a crowded market where experienced players usually want to play at the highest possible level."