Gibson intends to honour a gentleman's agreement - reached when Tottenham's £15million bid for the player was rejected in January - to let Downing leave if the 'right club' comes calling.
His comments come as Downing faces up to six months on the sidelines as he recovers from foot surgery.
Gibson said: "Stewart has been fantastic. He has given us 100 per cent commitment.
"He has suffered - he has suffered as a result of the performances, he has suffered because of the results and he is hurting.
Unsaid agreement"We had an unsaid agreement that if the right club came in - and I believe Stewart is a top four club player - we would not stand in his way.
"But Stewart was sad - he would be sad to leave our club.
"The injury he has got is going to take a substantial period of time - we think somewhere between four and six months.
"He is a great lad and I just want to see him back on the pitch enjoying his football, pressing for the England squad and if a big club comes in for him, I have given Stewart my word that I wouldn't stand in his way."