Alex Oxlade-Chamberlain reportedly had a clause in his contract that meant Arsenal would have to pay Southampton £10,000 every time he played 20 minutes or more.
Oxlade-Chamberlain signed for Arsenal in 2011 as a 17-year-old for a fee of around £12m with another £3m in add-ons.
The 25-year-old made 198 appearances for the Gunners before his transfer to Liverpool in 2017, with 80 of those coming from the substitutes bench.
Arsene Wenger often used Oxlade-Chamberlain as an impact player towards the end of matches.
Writer Alan Gernon has suggested, in his book The Transfer Market: The Inside Stories that was published in December, that a clause in his contract was the reason why he was used in that way.
He writes: “Following Alex Oxlade-Chamberlain’s move to Arsenal in 2011, Gunners fans became increasingly frustrated with the midfielder’s lack of playing time.
“He was predominantly used as a substitute, often around the 71-minute mark.
“After his contract details emerged, it all became clear: Arsenal were obliged to pay Southampton £10,000 every time he played 20 minutes or more.”
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Oxlade-Chamberlain has been out injured since April after suffering a serious knee injury against Roma in the Champions League semi-final.
Jurgen Klopp confirmed on Friday that he looks set to return to full training at the end of February.
The came after the player shared a picture of himself running on grass at the club’s Melwood training ground earlier this week.
Speaking on Friday, Klopp said: “Best news. He started going on the pitch and looked normal. We had to wait for the reaction and there was none.
“No pressure for him so late February/March for him to come back to training.”