The Tractor Boys fell to a surprise 1-0 loss at the hands of the Royals, although the damage was limited by fellow automatic promotion hopefuls Middlesbrough and Bournemouth also losing.
Conversely, a victory would lift them back into third place, with Bournemouth not playing until Wednesday night, when they face a tricky test away to a revitalised Nottingham Forest side.
Ipswich need to rediscover their form sooner rather than later, though, with 2015 proving to be an unhappy year for them so far. They have won just three of their 10 outings in all competitions since the turn of the year, dropping valuable points to four teams inside the bottom half.
Indeed, perhaps the most damaging thing about their recent form is that it has come in a relatively kind run of fixtures. Nine of their remaining 13 games after Tuesday come against sides in the top half, including a derby against Norwich City on Sunday.
The Tractor Boys can't afford to have one eye on gaining revenge on their East Anglian rivals, however, particularly considering that they have won just one of their last five home games in all competitions, failing to score in four of them.
That is a drastic dip in form for a side who had the best home record in the league before Saturday's defeat to Reading, already their second home league loss of 2015 having only recorded three throughout the whole of 2014.
McCarthy named an unchanged side at the weekend and could do the same again, with no new injury concerns having arisen from Saturday's fixture.
However, the hosts will still be without David McGoldrick due to a thigh injury, while Darren Ambrose (hamstring), Noel Hunt (knee), Stephen Hunt (hamstring) and Luke Hyam (knee) also remain sidelined.
Ipswich will feel that this is a good time to face Birmingham, whose promising start under Gary Rowett has ground to a halt in recent weeks.
A run of seven league matches without a win has seen the Blues slide back into the bottom half of the table and, while eight points still separate them from the relegation zone, there may be a few nervous glances over their shoulders if things don't improve soon.
Birmingham haven't been winless in eight league games since April 2010, and even their usually sturdy defence failed them at the weekend as they were beaten by relegation-threatened Brighton & Hove Albion.
Rowett's side had conceded just four goals in their previous six league matches but matched that total in 90 minutes at The Amex, going down 4-3 in a thrilling encounter.
That continued the club's search for an away victory this calendar year, although it was also their first loss on the road since the opening week of December.
Rob Kiernan made his debut in the defeat and should continue in the middle of the park with David Davis still out with a knee injury, while Koby Arthur is also unavailable due to a thigh injury sustained in training.
Clayton Donaldson is once again expected to lead the line, having scored for the first time in eight matches at the weekend.
Recent form: LDLWWL
Possible starting lineup: Bialkowski; Chambers, Smith, Berra, Mings; Bishop, Skuse, Bru, Tabb; Sears, Murphy
Possible starting lineup: Randolph; Caddis, Spector, Robinson, Grounds; Gleeson, Kiernan, Gray, Shinnie, Novak; Donaldson
Sports Mole says: 2-0