The 21-year-old striker still has two weeks left to run on his current agreement at Fratton Park, but has returned to parent employers Millwall as he has not yet been cleared to play in the FA Cup.
He packed his bags for London after being informed that he would form no part of Pompey's matchday squad for Saturday's 3-2 victory over Exeter.
The sight of him heading back to The Den with his belongings was taken by some as an indication that he would not be back.
Marquis has, however, taken to Twitter to express his desire to return to Portsmouth in the near future and fight for a place in Guy Whittingham's plans.
He said: "Just to clear things up, I am still very much a Pompey player for the remainder of my loan period.
"I was obviously bitterly disappointed not to be involved at the weekend, but by no means walked out in a strop and there wasn't any disagreement with the manager.
"The plan was to go back to Millwall to talk to the management and decide what was best for me. This is the reason I was seen leaving with all my belongings at the game on the weekend, just in case I didn't come back!
"If selected I will always put in 100 per cent for Portsmouth and show a professional attitude selected or not."