BBC Wiltshire report the 23-year-old forward left Sixfields before kick-off, having been told he wasn't involved in the squad for the League One match.
Head coach Luke Williams said the matter would be dealt with "in house".
The Robins are in the relegation zone after five straight losses, four points from safety, with 14 matches remaining.
Swindon have won three, drawn four and lost 11 of their 18 games in all competitions since Tim Sherwood's appointment as director of football on 10 November.

Yorkshire Water said the problem was detected at water treatment works at Tophill Low and Keldgate.
A spokesman said the issue had now been resolved but it could take several hours for water supplies to return to normal.
The HU7 and HU8 postcodes were particularly affected by the problem, along with other places in the city.
Tens of thousands of residents could be affected, but the exact figure will not be known until an investigation has been carried out.
Yorkshire Water said: "We apologise for the inconvenience caused this morning and hope to get the issue resolved and the water supply back to normal by the end of the day."

The scheme would be paid for by cutting the winter fuel allowance and free TV licences for better-off pensioners, the party's "pre-manifesto" proposes.
Mr Clegg told reporters: "We are telling you today that we are choosing to put the next generation front and centre of our plans."
The proposals are part of the Lib Dem pitch for next year's general election.
The Lib Dem leader, who became the target of angry students for performing a U-turn on tuition fees after entering government in 2010, said: "Liberal Democrats are committed to building a stronger economy and a fairer society, enabling people to get on in life.
"The Young Person's Bus Pass will ensure that young people looking to access education or training can do so in an affordable way, and I hope that bus companies will top up that discount to something even more generous."
The deputy PM added: "Young people are required to stay in school until they are 18, but we haven't done enough to give them the support that they need to do that - literally to help them get from A to B."
He rejected reports that free bus travel for pensioners would be axed by the Lib Dems if they got into power "not least because these bus passes help keep the buses running, and because we know how much older people rely on public transport".
But he did confirm that the young people's bus passes would be paid for by removing the free TV licences and winter fuel allowance from pensioners paying higher rate tax.
"I know there are people who say you mustn't touch so-called universal pensioner benefits because politically it's too risky. We don't agree. What are effectively benefits for the rich and retired cannot be justified when there are so many young people struggling to get on their feet."
Other measures in the Lib Dems' 80-page document include 15 hours of free childcare for every two-year-old in England, a "Daddy month" of paternity leave and guaranteed education spending.
The party is also promising to end imprisonment for people found carrying a small amount of drugs for personal use and to set up a commission to assess the effectiveness of current drugs laws and alternative approaches, including punishment by civil penalties rather than a criminal conviction and the case for licensed cannabis shops.
All the plans are subject to approval by the party's annual conference in Glasgow in October, but are likely to form the bulk of the party's campaign manifesto next year.
Mr Clegg said the party's proposals were "credible and deliverable", saying: "We've learnt our lesson from tuition fees - and we've learnt it the hard way. There will be no repeat of that mistake."
Labour's deputy leader Harriet Harman said: "Nick Clegg has once again shown what we all know - his government has let down working people. People will judge the Lib Dems on their record of broken promises and failure.
"What the Lib Dems say now is no guide to what they'll do in the future."
Swindon Town's Jermaine Hylton may face internal disciplinary action after walking out on his side before Tuesday's 2-1 loss at Northampton Town.
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Thousands of homes in Hull have been left without water due to a technical fault.
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Young people aged 16-21 would get a 66% discount on bus travel in England under Lib Dem plans outlined by Nick Clegg.