Man Utd speak to Alejandro Garnacho over controversial social media activity
The Argentina international, taken off at half-time in their 2-2 draw at Bournemouth on Saturday, liked two messages on X, by United fan and YouTuber Mark Goldbridge.
One post accused Ten Hag of "throwing (Garnacho) under the bus" because of comments the United boss made about the winger's performance.
The other said Garnacho "had a poor first half but taking him off at half time and holding him up as the problem is a joke".
Garnacho swiftly "unliked" both messages, an action the club believes shows contrition, and a United source told the PA news agency the matter had been dealt with internally.
The teenager has become a key player for United this season, scoring nine goals and providing four assists in 42 games.
The incident follows one in September when Jadon Sancho said on X that he had been made a "scapegoat" after being left out of the squad for the Arsenal match, with Ten Hag saying he had trained poorly.
Sancho said he would "not allow people saying things that (are) completely untrue", interpreted as accusing Ten Hag of misrepresenting reasons why he was not in the side.
The 24-year-old was banished from the first team before being loaned to Borussia Dortmund in January.
Ten Hag's position has come under renewed pressure after the draw against Bournemouth, which left United seventh in the Premier League table, 13 points off the top four.
The FA Cup is the only silverware that United can win this season - they take on second-tier side Coventry in the semi-final at Wembley on Sunday.
