"Scotty will be here for another year," he said. "He has been a good player since he walked in the door. It's a big boost for the squad.
“He has made a big contribution in the goals column and that football intelligence and experience is always important to have around.
"There is a familiarity there for Scott going into the Champions League qualifiers next season. He is one we don't need to replace."
However, the new report suggests all might not be exactly as it seems as the decision to sell Sinclair could be taken out of his hands with Celtic looking to recoup some money on a player they signed from Aston Villa for £3.5million in 2016.
Celtic boss Neil Lennon said he was delighted Scott Sinclair had extended his contract (Image: GETTY)
Sinclair has significant experience in the Championship and Tony Pulis could look to sign him if they fail to secure promotion this season.
Boro are currently seventh in the table, one point behind Derby in the final play-off spot.
They need to win at already-relegated Rotherham on the final day and hope Derby drop points at home against West Brom to make the play-offs.
Meanwhile, Celtic are preparing themselves for a busy summer as Lennon prepares for his first full season since returning as manager.
Sinclair could reportedly still leave the club in the summer (Image: GETTY)
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Sinclair has been linked with a move to Tony Pulis' Middlesbrough (Image: GETTY)
Lennon recently revealed in-demand left-back Kieran Tierney will need a hernia operation in the summer after missing a big chunk of Celtic’s games since the turn of the year.
Tierney is in contention to play against Aberdeen on Saturday but will need to have surgery at the end of the season.
And that will almost certainly mean he misses Scotland’s Euro 2020 qualifiers against Cyprus and Belgium in June.
"I think it will be very difficult for him to go with Scotland," Lennon said.
"We have sort of managed him on a daily basis and he is going to require surgery and the sooner the season finishes and he gets surgery the better it will be for him going forward and [the timescale] is probably three to four weeks."