According to reports, Celtic manager Brendan Rodgers and the club’s chief executive Peter Lawwell are ‘stunned’ by Regan signing off on a long-haul trip for Scotland to face Peru and Mexico in the Americas on May 29 and June 2.

With as many as eight Celtic players likely to be named among the travelling squad, Rodgers and Lawwell are understood to be concerned at the lack of a summer break for such a large number of Hoops players.

However, should Celtic win the Scottish Premiership title they will begin their Champions League qualifications campaign as early as July 10.

Celtic chief executive Peter Lawwell is planning on writing to Stewart Regan. Picture: SNS Group

And Parkhead skipper Scott Brown has already expressed concerns over the lack of a break, saying: “Last year we got six days and came back in and went straight into the Champions League qualifiers. We will probably get a week and a half this year.”

Celtic No. 2 Chris Davies echoed Brown’s comments, adding: “You do need a break. You cannot play 12 months non-stop and expect at a big club, the level of intensity, you want to be in the Champions League, it is impossible for players to play for 12 months.”

Lawwell is expected to write to Regan, calling for an explanation over the scheduling of the friendly matches.

Stewart Regan is believed to have upset Celtic. Picture: John Devlin

The Daily Record reports that Celtic should receive the backing of Scotland’s Professional Footballers’ Association (PFA Scotland).

Players’ union chiefs are said to be concerned at the shortening of the summer break and are expected to raise objections to the planned friendlies.

If Celtic reach the Scottish Cup final, their last match of the current campaign would take place on May 19, giving the club’s Scotland contingent fewer than ten days between the final and the Peru friendly.

And a revamp of the Champions League structure means that Celtic potentially face an additional round of qualifiers.

With Rodgers earmarking the second week of June for the start of pre-season training, the eight Scots would get a summer break of less than a fortnight if they travelled to the Americas.

A source told the Record: “When you look at that schedule, it’s no wonder that Rodgers and Lawwell have been infuriated by the SFA’s decision to take on this tour.

“Celtic’s players have made a big contribution to the national team over the last 12 months and this is the way they have been rewarded? It defies belief that Regan didn’t even discuss this with the club.”

Celtic accuse Stewart Regan of '˜jeopardising Champions League' hopes