Is it pay on day tomorrow?

No reason why not.

Selling times are only limited for the “big boys”. You’ll be able to buy at the ticket office (West or East Stand) tomorrow.

Website says:

Ticket information for the visit of Southampton to the DW Stadium on Saturday 2 February

Wigan Athletic v Southampton
Barclays Premier League
Saturday 2 February 2013, kick off 3.00pm
DW Stadium

Wigan Athletic host Southampton in the Barclays Premier League at the DW Stadium on Saturday 2 February 2013 at 3.00pm.

Tickets are on sale now for this game which is a category C fixture with adult tickets available from just £20 and juniors from just £5.

For this game, Team Latics are giving junior supporters the chance to bring a friend for free. [Click here] for full details.

Ticket Prices
Adults (central areas) £22.00
Adults (all other areas) £20.00
Over 65 / Disabled (central areas) £17.00
Over 65 / Disabled (all other areas) £15.00
Under 16s (central areas) £7.00
Under 16s (all other areas) £5.00
Tickets are available from the DW Stadium ticket office during normal office hours. Tickets are also available online by clicking here and you can call the ticket hotline on 0871 66 33 552*.