Reading must pay Cork City a further £17,000 after Kevin Doyle made his international debut last week.
Doyle was replaced after 68 minutes on his international debut
The 22-year-old striker played for the Republic of Ireland in their 3-0 win over Sweden at Lansdowne Road.
Director of football Nick Hammond said: "We signed Kevin for little under £80,000 in the summer and he's repaid us with 15 goals so far this season.
"We have to pay Cork a bit more now he's an international, but we're happy to hand over the money."