The versatile winger is currently enjoying a rich vein of form, scoring four goals in his last five outings.
Starting his career in his native Ireland, spells at Bray Wanderers and Gallaway United attracted O'Shea a move to Birmingham in 2009.
After struggling to break to into the first-team setup at St Andrew's, the midfielder had brief spells on loan at Middlesborough, Stevenage and Port Vale, before a permanent move to MK Dons in 2011.
The twenty-eight-year-old originally arrived at the Proact Stadium on loan in November 2012, before making the switch permanent in January 2013.
O'Shea played at Wembley in Chesterfield's defeat to Peterborough United in the Football League Trophy back in 2014 and has since made over one-hundred-and-seventy appearances for the club.
The twenty-one-year-old is a loanee at the Proact Stadium from Bolton Wanderers and so far has four goals to his name so far during his loan spell.
After starting his career at Millwall, the striker progressed through the ranks during his three-year spell with the South-London club. In 2013 the forward joined Bolton Wanderers and initially went into their reserve squad, before loan moves to Chester, Torquay United, Oldham Athletic, and Barnsley.
Last season the striker experienced loan moves at both Newport County and Portsmouth and joined Chesterfield on loan until January towards the end of August, with the forward bagging four goals in the month of September.
The youngster has also been capped at both U19 and U21 level for the Republic of Ireland.
A twenty-six-year-old Irish striker, Dennis is a new arrival at Chesterfield this season following his arrival from Stockport County.
The forward began his career at Macclesfield Town and has since forged a career in non-league football, taking in spells at Woodley Sports, Mossley and Curzon Ashton, before joining Stockport in June 2013.
The striker spent last season on loan at Macclesfield 23 goals in 39 appearances, which caught the attention of Chesterfield, who signed the striker in May.
So far this campaign the striker has six goals to his name in all competitions and scored in Chesterfield's 3-2 victory against MK Dons on Tuesday evening.