Celtic manager Martin O'Neill has admitted he is disappointed to see Arne Engels leave the club, but acknowledged the midfielder had little choice but to accept West Ham's offer — a five-year deal worth £22 million.

Engels departs for West Ham despite Celtic having turned down a £25 million bid from Nottingham Forest for the Belgium international during the January transfer window. O'Neill noted that Engels never complained when that offer came in late and was ultimately rejected.

"Naturally disappointed, really, that he's leaving the football club, he's done very well for us. It's an opportunity for him and it's really hard for him to turn it down," O'Neill said.

The 74-year-old manager was speaking at a press conference ahead of Celtic's Scottish League Cup second-round tie against Dundee United on Saturday. Engels' exit also comes just before Celtic's UEFA Champions League play-off first leg against LASK next Wednesday.

Johnston injury adds to Celtic's concerns

O'Neill also revealed that right-back Alistair Johnston will miss several weeks after suffering a leg muscle injury. Johnston was substituted at half-time during Celtic's 5-1 victory over Kilmarnock on Sunday, with Everton having shown interest in the Canada international.

The manager suggested Engels may have had Johnston's situation in mind when pushing for an early departure — wary that a similar injury could derail his own transfer.

"I suppose Arne was probably worried the same sort of thing might happen. From a playing viewpoint, I probably can understand that," O'Neill said.

On Johnston, O'Neill struck an upbeat tone: "He'll be out for a few weeks. By the time he's fit, he'll be past the transfer deadline. It's a shame for him but it's not long-term."

More arrivals expected at Celtic Park

Celtic have already moved quickly in the market this week, bringing in Egypt winger Haissem Hassan and Germany Under-21 midfielder Mika Baur. O'Neill indicated further signings are on the way before the window shuts.

One potential addition is Chelsea left-back Landon Emenalo, who is 18 years old and was shown around Celtic's Lennoxtown training centre this week. The teenager is being considered as a loan option to provide cover for Kieran Tierney.

"I think he's a really fine young player. Obviously we need that position covered. He's got a bit of an injury at the moment — we're hoping that will clear up shortly. And if it does, I'd love to have him," O'Neill said.

O'Neill, who is fully back at work following a medical procedure last week, praised Tierney's remarkable return to form after his injury struggles at Arsenal, and made clear that adding depth at left-back remains a priority for Celtic before the window closes.