Morocco international Benatia has been linked with Manchester City, Chelsea and several other clubs on the back of an impressive first season at Roma following his move from Udinese.
The 27-year-old is reported to be unsettled, but Garcia has no intention of allowing him to leave and revealed he will play in a pre-season friendly against Liverpool at Fenway Park in Boston on Wednesday.
"Mehdi is under contract and will play with Roma this season," he said on Tuesday.
"Fortunately the president manages to speak to all the players and yesterday he talked to everyone.
"Tomorrow Benatia will play against Liverpool."
Serbia international Ljajic has also been the subject of transfer speculation ahead of the new season, particularly following the arrival of Juan Iturbe from Verona last week.
Garcia has also played down talk of Ljajic departing as the Frenchman attempts to build on an impressive first season at the helm.
"For me the primary transfer strategy is to keep our most important players and Adem is one of them," Garcia said. "He takes a lot of responsibility on his shoulders and I like that.
"We have to be wary of not putting too much pressure on Iturbe. He can improve and will be important in attack, but it'll take a while before we see him at his best in our system."
Roma finished second in Serie A last season, achieving their highest top-flight points tally of 85.