Slocombe, 23, whose only start for the club came in the Carling Cup win over Oldham last season, will deputise if Sam Johnstone - himself brought in on loan following an injury to first-choice keeper Josh Lillis - is ruled out due to a dislocated finger.
Johnstone, borrowed from the Premier League champions Manchester United, suffered the injury in training on Monday.
United also have doubts over Damien Mozika (ankle) and Eddie Nolan (calf). Andrew Wright serves a one-match suspension having been sent-off in last weekend's goalless draw at Brentford.
Matt Godden (hip/hernia), Jordan Robertson (ankle) and Jimmy Ryan (knee) remain out. Cliff Byrne (back) and Michael Collins (tendonitis) are back in full training but not considered ready for first-team football yet.
Karl Robinson, the MK Dons boss, has a virtually full-strength squad to choose from. Midfielder Jay O'Shea (ankle) is his only absentee.